Documentation |
GUI-based filter design
filterbuilder(h)
filterbuilder('response')
filterbuilder starts a GUI-based tool for building filters. It relies on the fdesign object-object oriented filter design paradigm, and is intended to reduce development time during the filter design process. filterbuilder uses a specification-centered approach to find the best algorithm for the desired response.
Note: You must have the Signal Processing Toolbox™ installed to use fdesign and filterbuilder. Some of the features described below may be unavailable if your installation does not additionally include the DSP System Toolbox™. You can verify the presence of both toolboxes by typing ver at the command prompt. |
The filterbuilder GUI contains many features not available in FDATool. For more information on how to use filterbuilder, see Filterbuilder Design Process.
To use filterbuilder, enter filterbuilder at the MATLAB^{®} command line using one of three approaches:
Simply enter filterbuilder. MATLAB opens a dialog for you to select a filter response type. After you select a filter response type, filterbuilder launches the appropriate filter design dialog box.
Enter filterbuilder(h), where h is an existing filter object. For example, if h is a bandpass filter, filterbuilder(h) opens the bandpass filter design dialog box. (The h object must have been created using filterbuilder or must be a dfilt ,mfilt, or filter System object created using fdesign.)
Enter filterbuilder('response'), replacing response with a response string from the following table. MATLAB opens a filter design dialog that corresponds to the response string.
Note: You must have the DSP System Toolbox software to implement a number of the filter designs listed in the following table. If you only have the Signal Processing Toolbox software, you can design a limited set of the following filter-response types. |
Response String | Description of Resulting Filter Design | Filter Object |
---|---|---|
arbgrpdelay | Arbitrary group delay filter design | fdesign.arbgrpdelay |
arbmag | Arbitrary magnitude filter design | fdesign.arbmag |
arbmagnphase | Arbitrary response filter (magnitude and phase) | fdesign.arbmagnphase |
audioweighting | Audio weighting filter | fdesign.audioweighting |
bandpass or bp | Bandpass filter | fdesign.bandpass |
bandstop or bs | Bandstop filter | fdesign.bandstop |
cic | CIC filter | fdesign.decimator(M,'cic',...) or fdesign.interpolator(L,'cic',...) See fdesign.decimator and fdesign.interpolator |
ciccomp | CIC compensator | fdesign.ciccomp |
comb | Comb filter | fdesign.comb |
diff | Differentiator filter | fdesign.differentiator |
fracdelay | Fractional delay filter | fdesign.fracdelay |
halfband or hb | Halfband filter | fdesign.halfband |
highpass or hp | Highpass filter | fdesign.highpass |
hilb | Hilbert filter | fdesign.hilbert |
isinc, isinclp, or isinchp | Inverse sinc lowpass or highpass filter | fdesign.isinclp and fdesign.isinchp |
lowpass or lp | Lowpass filter (default) | fdesign.lowpass |
notch | Notch filter | fdesign.notch |
nyquist | Nyquist filter | fdesign.nyquist |
octave | Octave filter | fdesign.octave |
parameq | Parametric equalizer filter | fdesign.parameq |
peak | Peak filter | fdesign.peak |
Note: Because they do not change the filter structure, the magnitude specifications and design method are tunable when using filterbuilder. |
The main pane of filterbuilder varies depending on the filter response type, but the basic structure is the same. The following figure shows the basic layout of the dialog box.
As you choose the response for the filter, the available options and design parameters displayed in the dialog box change. This display allows you to focus only on parameters that make sense in the context of your filter design.
Every filter design dialog box includes the options displayed at the top of the dialog box, shown in the following figure.
Save variable as — When you click Apply to apply your changes or OK to close this dialog box, filterbuilder saves the current filter to your MATLAB workspace as a filter object with the name you enter.
View Filter Response — Displays the magnitude response for the current filter specifications and design method by opening the Filter Visualization Tool (fvtool).
Note: The filterbuilder dialog box includes an Apply option. Each time you click Apply, filterbuilder writes the modified filter to your MATLAB workspace. This modified filter has the variable name you assign in Save variable as. To apply changes without overwriting the variable in you workspace, change the variable name in Save variable as before you click Apply. |
There are three tabs in the Filterbuilder dialog box, containing three panes: Main, Data Types, and Code Generation. The first pane changes according to the filter being designed. The last two panes are the same for all filters. These panes are discussed in the following sections.
The second tab in the Filterbuilder dialog box is shown in the following figure.
The Arithmetic drop down box allows the choice of Double precision, Single precision, or Fixed point. Some of these options may be unavailable depending on the filter parameters. The following table describes these options.
Arithmetic List Entry | Effect on the Filter |
---|---|
Double precision | All filtering operations and coefficients use double-precision, floating-point representations and math. When you use filterbuilder to create a filter, double precision is the default value for the Arithmetic property. |
Single precision | All filtering operations and coefficients use single-precision floating-point representations and math. |
Fixed point | This string applies selected default values, typically used on many digital processors, for the properties in the fixed-point filter. These properties include coefficient word lengths, fraction lengths, and various operating modes. This setting allows signed fixed data types only. Fixed-point filter design with filterbuilder is available only when you install Fixed-Point Designer™ software along with DSP System Toolbox software. |
The following figure shows the Data Types pane after you select Fixed point for Arithmetic and set Filter internals to Specify precision. This figure shows the Data Types pane for the case where the Use a System object to implement filter check box is not selected in the Main pane.
Not all parameters described in the following section apply to all filters. For example, FIR filters do not have the Section input and Section output parameters.
Specify the format the filter applies to data to be filtered. For all cases, filterbuilder implements filters that use binary point scaling and signed input. You set the word length and fraction length as needed.
Choose how you specify the word length and the fraction length of the filter numerator and denominator coefficients:
Specify word length enables you to enter the word length of the coefficients in bits. In this mode, filterbuilder automatically sets the fraction length of the coefficients to the binary-point only scaling that provides the best possible precision for the value and word length of the coefficients.
Binary point scaling enables you to enter the word length and the fraction length of the coefficients in bits. If applicable, enter separate fraction lengths for the numerator and denominator coefficients.
The filter coefficients do not obey the Rounding mode and Overflow mode parameters that are available when you select Specify precision from the Filter internals list. Coefficients are always saturated and rounded to Nearest.
Choose how you specify the word length and the fraction length of the fixed-point data type going into each section of an SOS filter. This parameter is visible only when the selected filter structure is IIR and SOS.
Binary point scaling enables you to enter the word and fraction lengths of the section input in bits.
Specify word length enables you to enter the word lengths in bits.
Choose how you specify the word length and the fraction length of the fixed-point data type coming out of each section of an SOS filter. This parameter is visible only when the selected filter structure is IIR and SOS.
Binary point scaling enables you to enter the word and fraction lengths of the section output in bits.
Specify word length enables you to enter the output word lengths in bits.
Contains the filter states before, during, and after filter operations. States act as filter memory between filtering runs or sessions. Use this parameter to specify how to designate the state word and fraction lengths. This parameter is not visible for direct form and direct form I filter structures because filterbuilder deduces the state directly from the input format. States always use signed representation:
Binary point scaling enables you to enter the word length and the fraction length of the accumulator in bits.
Specify precision enables you to enter the word length and fraction length in bits (if available).
Determines how the filter handles the output of product operations. Choose from the following options:
Full precision — Maintain full precision in the result.
Keep LSB — Keep the least significant bit in the result when you need to shorten the data words.
Specify Precision — Enables you to set the precision (the fraction length) used by the output from the multiplies.
Specify how the fixed-point filter performs arithmetic operations within the filter. The affected filter portions are filter products, sums, states, and output. Select one of these options:
Full precision — Specifies that the filter maintains full precision in all calculations for products, output, and in the accumulator.
Specify precision — Set the word and fraction lengths applied to the results of product operations, the filter output, and the accumulator. Selecting this option enables the word and fraction length controls.
Selecting this option directs the filter to use signed representations for the filter coefficients.
Sets the word length for the associated filter parameter in bits.
Sets the fraction length for the associate filter parameter in bits.
Use this parameter to specify how you would like to designate the accumulator word and fraction lengths.
Determines how the accumulator outputs stored values. Choose from the following options:
Full precision — Maintain full precision in the accumulator.
Keep MSB — Keep the most significant bit in the accumulator.
Keep LSB — Keep the least significant bit in the accumulator when you need to shorten the data words.
Specify Precision — Enables you to set the precision (the fraction length) used by the accumulator.
Sets the mode the filter uses to scale the output data after filtering. You have the following choices:
Avoid Overflow — Set the output data fraction length to avoid causing the data to overflow. Avoid overflow is considered the conservative setting because it is independent of the input data values and range.
Best Precision — Set the output data fraction length to maximize the precision in the output data.
Specify Precision — Set the fraction length used by the filtered data.
Parameters in this group control how the filter rounds fixed-point values and how it treats values that overflow.
Sets the mode the filter uses to quantize numeric values when the values lie between representable values for the data format (word and fraction lengths).
ceil - Round toward positive infinity.
convergent - Round to the closest representable integer. Ties round to the nearest even stored integer. This is the least biased of the methods available in this software.
zero/fix - Round toward zero.
floor - Round toward negative infinity.
nearest - Round toward nearest. Ties round toward positive infinity.
round - Round toward nearest. Ties round toward negative infinity for negative numbers, and toward positive infinity for positive numbers.
The choice you make affects everything except coefficient values and input data which always round. In most cases, products do not overflow—they maintain full precision.
Sets the mode the filter uses to respond to overflow conditions in fixed-point arithmetic. Choose from the following options:
Saturate — Limit the output to the largest positive or negative representable value.
Wrap — Set overflowing values to the nearest representable value using modular arithmetic.
The choice you make affects everything except coefficient values and input data which always round. In most cases, products do not overflow—they maintain full precision.
Specifies whether to cast numeric data to the appropriate accumulator format before performing sum operations. Selecting Cast before sum ensures that the results of the affected sum operations match most closely the results found on most digital signal processors. Performing the cast operation before the summation adds one or two additional quantization operations that can add error sources to your filter results.
If you clear Cast before sum, the filter prevents the addends from being cast to the sum format before the addition operation. Choose this setting to get the most accurate results from summations without considering the hardware your filter might use. The input format referenced by Cast before sum depends on the filter structure you are using.
The effect of clearing or selecting Cast before sum is as follows:
Cleared — Configures filter summation operations to retain the addends in the format carried from the previous operation.
Selected — Configures filter summation operations to convert the input format of the addends to match the summation output format before performing the summation operation. Usually, selecting Cast before sum generates results from the summation that more closely match those found from digital signal processors.
The code generation pane contains options for various implementations of the completed filter design. Depending on your installation, you can generate MATLAB, VHDL, and Verilog code from the designed filter. You can also choose to create or update a Simulink^{®} model from the designed filter. The following section explains these options.
For more information on this option, see Opening the Filter Design HDL Coder GUI From the filterbuilder GUI.
Generate MATLAB code based on filter specifications
Generate function that returns your filter as an output
Selecting this option generates a function that designs either a DFILT/MFILT object or a system object (depending on whether you have selected the Use a System object to implement the filter check box) using fdesign. The function call returns a filter object.
Generate function that filters your data
Selecting this option generates a function that takes data as input, and outputs data filtered with the designed filter.
Clicking on the Generate MATLAB code button, brings up a Save File dialog. Specify the file name and location, and save. The filter is now contained in an editable file.
Generate Simulink blocks and subsystems from your designed filters
When the Use a System object to implement filter check box is selected in the Main pane, you are able to generate Simulink models as long as the Arithmetic is not set to Fixed point in the Data Types pane. If the Arithmetic is set to Fixed point, the Generate Model button in the Simulink model panel will be disabled.
Clicking on the Generate Model button brings up the Export to Simulink dialog box, as shown in the following figure.
You can set the following parameters in this dialog box:
Block Name — The name for the new subsystem block, set to Filter by default.
Destination — Current saves the generated model to the current Simulink model; New creates a new model to contain the generated block; User Defined creates a new model or subsystem to the user-specified location enumerated in the User Defined text box.
Overwrite generated 'Filter' block — When this check box is selected, DSP System Toolbox software overwrites an existing block with the name specified in Block Name; when cleared, creates a new block with the same name.
Build model using basic elements — When this check box is selected, DSP System Toolbox software builds the model using only basic blocks.
Optimize for zero gains — When this check box is selected, DSP System Toolbox software removes all zero gain blocks from the model.
Optimize for unity gains — When this check box is selected, DSP System Toolbox software replaces all unity gains with direct connections.
Optimize for negative gains — When this check box is selected, DSP System Toolbox software removes all negative unity gain blocks, and changes sign at the nearest summation block.
Optimize delay chains — When this check box is selected, DSP System Toolbox software replaces delay chains made up of n unit delays with a single delay by n.
Optimize for unity scale values — When this check box is selected, DSP System Toolbox software removes all scale value multiplications by 1 from the filter structure.
Input processing — Specify how the generated filter block or subsystem block processes the input. Depending on the type of filter you are designing, one or both of the following options may be available:
Columns as channels (frame based) — When you select this option, the block treats each column of the input as a separate channel.
Elements as channels (sample based) — When you select this option, the block treats each element of the input as a separate channel.
For more information about sample- and frame-based processing, see Sample- and Frame-Based Concepts.
Realize Model — DSP System Toolbox software builds the model with the set parameters.
Select your filter response from the filterbuilder Response Selection main menu.
If you have the DSP System Toolbox software, the following Response Selection menu appears.
Select your desired filter response from the menu and design your filter.
The following sections describe the options available for each response type.
Parameters in this group enable you to specify your filter format, such as the impulse response and the filter order.
This dialog only applies if you have the DSP System Toolbox software. Select either FIR or IIR from the drop down list, where FIR is the default impulse response. When you choose an impulse response, the design methods and structures you can use to implement your filter change accordingly. Arbitrary group delay designs are only available if Impulse response is IIR. Without the DSP System Toolbox, the only available arbitrary response filter design is FIR.
This dialog only applies if you have the DSP System Toolbox software. Choose Minimum or Specify. Choosing Specify enables the Order dialog.
This dialog only applies when Order mode is Specify. For an FIR design, specify the filter order. For an IIR design, you can specify an equal order for the numerator and denominator, or you can specify different numerator and denominator orders. The default is equal orders. To specify a different denominator order, check the Denominator order box. Because the Signal Processing Toolbox only supports FIR arbitrary-magnitude filters, you do not have the option to specify a denominator order.
Select the check box and enter the denominator order. This option is enabled only if IIR is selected for Impulse response.
This dialog only applies if you have the DSP System Toolbox software and is only available for FIR filters. Select Single-rate, Decimator, Interpolator, or Sample-rate converter. Your choice determines the type of filter as well as the design methods and structures that are available to implement your filter. By default, filterbuilder specifies single-rate filters.
Selecting Decimator or Interpolator activates the Decimation Factor or the Interpolation Factor options respectively.
Selecting Sample-rate converter activates both factors.
When you design either a decimator or interpolator, the resulting filter is a bandpass filter that either decimates or interpolates your input signal.
Enter the decimation factor. This option is enabled only if the Filter type is set to Decimator or Sample-rate converter. The default factor value is 2 for Decimator and 3 for Sample-rate converter.
Enter the decimation factor. This option is enabled only if the Filter type is set to Interpolator or Sample-rate converter. The default factor value is 2.
Select the number of bands in the filter. Multiband design is available for both FIR and IIR filters.
Specify the response as Amplitudes, Magnitudes and phase, Frequency response, or Group delay. Amplitudes is the only option if you do not have the DSP System Toolbox software. Group delay is only available for IIR designs.
Specify frequency units as either Normalized, Hz, kHz, MHz, or GHz.
Enter the input sampling frequency in the units specified in the Frequency units drop-down box. This option is enabled when Frequency units is set to an option in hertz.
These properties are modified automatically depending on the response chosen in the Specify response as drop-down box. Two or three columns are presented for input. The first column is always Frequencies. The other columns are either Amplitudes, Magnitudes, Phases, or Frequency Response. Enter the corresponding vectors of values for each column.
Frequencies and Amplitudes — These columns are presented for input if you select Amplitudes in the Specify response as drop-down box.
Frequencies, Magnitudes, and Phases — These columns are presented for input if the response chosen in the Specify response as drop-down box is Magnitudes and phases.
Frequencies and Frequency response — These columns are presented for input if the response chosen in the Specify response as drop-down box is Frequency response.
The options for each design are specific for each design method. In the arbitrary response design, the available options also depend on the Response specifications. This section does not present all of the available options for all designs and design methods.
Select the design method for the filter. Different methods are enabled depending on the defining parameters entered in the previous sections.
Window — Valid when the Design method is Frequency Sampling. Replace the square brackets with the name of a window function or function handle. For example, 'hamming' or @hamming. If the window function takes parameters other than the length, use a cell array. For example, {‘kaiser',3.5} or {@chebwin,60}.
Density factor — Valid when the Design method is equiripple. Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1).
Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 16 represents a reasonable trade between the accurate approximation to the ideal filter and the time to design the filter.
The default changes to 20 for an IIR arbitrary group delay design.
Phase constraint — Valid when the Design method is equiripple, you have the DSP System Toolbox installed, and Specify response as is set to Amplitudes. Choose one of Linear, Minimum, or Maximum.
Weights — Uses the weights in Weights to weight the error for a single-band design. If you have multiple frequency bands, the Weights design option changes to B1 Weights, B2 Weights to designate the separate bands. Use Bi Weights to specify weights for the i-th band. The Bi Weights design option is only available when you specify the i-th band as an unconstrained.
Bi forced frequency point — This option is only available in a multi-band constrained equiripple design when Specify response as is Amplitudes. Bi forced frequency point is the frequency point in the i-th band at which the response is forced to be zero. The index i corresponds to the frequency bands in Band properties. For example, if you specify two bands in Band properties, you have B1 forced frequency point and B2 forced frequency point.
Norm — Valid only for IIR arbitrary group delay designs. Norm is the norm used in the optimization. The default value is 128, which essentially equals the L-infinity norm. The norm must be even.
Max pole radius — Valid only for IIR arbitrary group delay designs. Constrains the maximum pole radius. The default is 0.999999. Reducing the Max pole radius can produce a transfer function more resistant to quantization.
Init norm — Valid only for IIR arbitrary group delay designs. The initial norm used in the optimization. The default initial norm is 2.
Init numerator — Specifies an initial estimate of the filter numerator coefficients.
Init denominator — Specifies an initial estimate of the filter denominator coefficients. This may be useful in difficult optimization problems. In allpass filters, you only have to specify either the denominator or numerator coefficients. If you specify the denominator coefficients, you can obtain the numerator coefficients.
Select the structure for the filter. The available filter structures depend on the parameters you select for your filter.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Weighting type — The weighting type defines the frequency response of the filter. The valid weighting types are: A, C , C-message, ITU-T 0.41, and ITU-R 468–4 weighting. See fdesign.audioweighting for definitions of the weighting types.
Class — Filter class is only applicable for A weighting and C weighting filters. The filter class describes the frequency-dependent tolerances specified in the relevant standards. There are two possible class values: 1 and 2. Class 1 weighting filters have stricter tolerances than class 2 filters. The filter class value does not affect the design. The class value is only used to provide a specification mask in fvtool for the analysis of the filter design.
Impulse response — Impulse response type as one of IIR or FIR. For A, C , C-message, and ITU-R 468–4 filter, IIR is the only option. For a ITU-T 0.41 weighting filter, FIR is the only option.
Frequency units — Choose Hz, kHz, MHz, or GHz. Normalized frequency designs are not supported for audio weighting filters.
Input Fs — The sampling frequency in Frequency units. For example, if Frequency units is set to kHz, setting Input Fs to 40 is equivalent to a 40 kHz sampling frequency.
Design method — Valid design methods depend on the weighting type. For type A and C weighting filters, the only valid design type is ANSI S1.42. This is an IIR design method that follows ANSI standard S1.42–2001. For a C message filter, the only valid design method is Bell 41009, which is an IIR design method following the Bell System Technical Reference PUB 41009. For a ITU-R 468–4 weighting filter, you can design an IIR or FIR filter. If you choose an IIR design, the design method is IIR least p-norm. If you choose an FIR design, the design method choices are: Equirriple or Frequency Sampling. For an ITU-T 0.41 weighting filter, the available FIR design methods are equirriple or Frequency Sampling
Scale SOS filter coefficients to reduce chance of overflow — Selecting this parameter directs the design to scale the filter coefficients to reduce the chances that the inputs or calculations in the filter overflow and exceed the representable range of the filter. Clearing this option removes the scaling. This parameter applies only to IIR filters.
Structure — For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. For audio weighting IIR filter designs, you can choose direct form I or II biquad (SOS). You can also choose to implement these structures in transposed form.
For FIR designs, you can choose direct form, direct-form transposed, direct-form symmetric, direct-form asymmetric structures, or an overlap and add structure.
Use a System object to implement filter — Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Parameters in this group enable you to specify your filter format, such as the impulse response and the filter order.
Select FIR or IIR from the drop-down list, where FIR is the default impulse response. When you choose an impulse response, the design methods and structures you can use to implement your filter change accordingly.
Select Minimum (the default) or Specify from the drop-down box. Selecting Specify enables the Order option so you can enter the filter order.
If you have the DSP System Toolbox software installed, you can specify IIR filters with different numerator and denominator orders. The default is equal orders. To specify a different denominator order, check the Denominator order box.
Select Single-rate, Decimator, Interpolator, or Sample-rate converter. Your choice determines the type of filter as well as the design methods and structures that are available to implement your filter. By default, filterbuilder specifies single-rate filters.
Selecting Decimator or Interpolator activates the Decimation Factor or the Interpolation Factor options respectively.
Selecting Sample-rate converter activates both factors.
Enter the filter order. This option is enabled only if you select Specify for Order mode.
Enter the decimation factor. This option is enabled only if the Filter type is set to Decimator or Sample-rate converter. The default factor value is 2.
Enter the decimation factor. This option is enabled only if the Filter type is set to Interpolator or Sample-rate converter. The default factor value is 2.
The parameters in this group allow you to specify your filter response curve. Graphically, the filter specifications look similar to those shown in the following figure.
In the figure, regions between specification values such as Fstop1 and Fpass1 represent transition regions where the filter response is not explicitly defined.
Select the filter features to use to define the frequency response characteristics. This dialog applies only when Order mode is Specify.
Passband and stopband edges — Define the filter by specifying the frequencies for the edges for the stop- and passbands.
Passband edges — Define the filter by specifying frequencies for the edges of the passband.
Stopband edges — Define the filter by specifying frequencies for the edges of the stopbands.
3dB points — Define the filter response by specifying the locations of the 3 dB points (IIR filters). The 3-dB point is the frequency for the point 3 dB below the passband value.
3dB points and passband width — Define the filter by specifying frequencies for the 3-dB points in the filter response and the width of the passband. (IIR filters)
3dB points and stopband widths — Define the filter by specifying frequencies for the 3-dB points in the filter response and the width of the stopband. (IIR filters)
6dB points — Define the filter response by specifying the locations of the 6-dB points. The 6-dB point is the frequency for the point 6dB below the passband value. (FIR filters)
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in hertz, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Enter the frequency at the edge of the end of the first stopband. Specify the value in either normalized frequency units or the absolute units you select in Frequency units.
Enter the frequency at the edge of the start of the passband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
Enter the frequency at the edge of the end of the passband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
Enter the frequency at the edge of the start of the second stopband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
The parameters in this group let you specify the filter response in the passbands and stopbands.
Specify as Unconstrained or Constrained bands. You must have the DSP System Toolbox software to select Constrained bands. Selecting Constrained bands enables dialogs for both stopbands and the passband: Astop1, Astop2, and Apass. You cannot specify constraints for all three bands simultaneously.
Setting Magnitude constraints to Constrained bands enables the Wstop and Wpass options under Design options.
Specify the units for any parameter you provide in magnitude specifications. Select one of the following options from the drop-down list.
Linear — Specify the magnitude in linear units.
dB — Specify the magnitude in dB (decibels). This is the default setting.
Squared — Specify the magnitude in squared units.
Enter the filter attenuation in the first stopband in the units you choose for Magnitude units, either linear or decibels.
Enter the filter ripple allowed in the passband in the units you choose for Magnitude units, either linear or decibels.
Enter the filter attenuation in the second stopband in the units you choose for Magnitude units, either linear or decibels.
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
Lists the design methods available for the frequency and magnitude specifications you entered. When you change the specifications for a filter, such as changing the impulse response, the methods available to design filters changes as well. The default IIR design method is usually Butterworth, and the default FIR method is equiripple.
Selecting this parameter directs the design to scale the filter coefficients to reduce the chances that the inputs or calculations in the filter overflow and exceed the representable range of the filter. Clearing this option removes the scaling. This parameter applies only to IIR filters.
Design Options
The options for each design are specific for each design method. This section does not present all of the available options for all designs and design methods. There are many more that you encounter as you select different design methods and filter specifications. The following options represent some of the most common ones available.
Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1).
Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 16 represents a reasonable trade between the accurate approximation to the ideal filter and the time to design the filter.
Valid when the Design method is equiripple and you have the DSP System Toolbox installed. Choose one of Linear, Minimum, or Maximum.
This option only applies when you have the DSP System Toolbox software and Order mode is Minimum.
Select Any (default), Even, or Odd. Selecting Even or Odd forces the minimum-order design to be an even or odd order.
Weight for the first stopband.
Passband weight.
Weight for the second stopband.
Valid only for IIR designs. Constrains the maximum pole radius. The default is 1. Reducing the max pole radius can produce a transfer function more resistant to quantization.
Valid only for IIR designs. The initial norm used in the optimization. The default initial norm is 2.
Specifies an initial estimate of the filter numerator coefficients. This may be useful in difficult optimization problems.
Specifies an initial estimate of the filter denominator coefficients. This may be useful in difficult optimization problems.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use direct-form structure, and IIR filters use direct-form II filters with SOS.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Parameters in this group enable you to specify your filter format, such as the impulse response and the filter order.
Select FIR or IIR from the drop-down list, where FIR is the default impulse response. When you choose an impulse response, the design methods and structures you can use to implement your filter change accordingly.
Select Minimum (the default) or Specify from the drop-down list. Selecting Specify enables the Order option so you can enter the filter order.
If you have the DSP System Toolbox software installed, you can specify IIR filters with different numerator and denominator orders. The default is equal orders. To specify a different denominator order, check the Denominator order box.
Select Single-rate, Decimator, Interpolator, or Sample-rate converter. Your choice determines the type of filter as well as the design methods and structures that are available to implement your filter. By default, filterbuilder specifies single-rate filters.
Selecting Decimator or Interpolator activates the Decimation Factor or the Interpolation Factor options respectively.
Selecting Sample-rate converter activates both factors.
When you design either a decimator or an interpolator, the resulting filter is a bandpass filter that either decimates or interpolates your input signal.
Enter the filter order. This option is enabled only if Specify was selected for Order mode.
Enter the decimation factor. This option is enabled only if the Filter type is set to Decimator or Sample-rate converter. The default factor value is 2.
Enter the decimation factor. This option is enabled only if the Filter type is set to Interpolator or Sample-rate converter. The default factor value is 2.
The parameters in this group allow you to specify your filter response curve. Graphically, the filter specifications look similar to those shown in the following figure.
Select the filter features to use to define the frequency response characteristics. This dialog applies only when Order mode is Specify.
Passband and stopband edges — Define the filter by specifying the frequencies for the edges for the stop- and passbands.
Passband edges — Define the filter by specifying frequencies for the edges of the passband.
Stopband edges — Define the filter by specifying frequencies for the edges of the stopbands.
3dB points — Define the filter response by specifying the locations of the 3 dB points (IIR filters). The 3 dB point is the frequency for the point 3 dB point below the passband value.
3dB points and passband width — Define the filter by specifying frequencies for the 3 dB points in the filter response and the width of the passband (IIR filters).
3dB points and stopband widths — Define the filter by specifying frequencies for the 3 dB points in the filter response and the width of the stopband (IIR filters).
6dB points — Define the filter response by specifying the locations of the 6-dB points (FIR filters). The 6-dB point is the frequency for the point 6 dB point below the passband value.
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
When you design an interpolator, Fs represents the sampling frequency at the filter output rather than the filter input. This option is available only when you set Filter type is interpolator.
Enter the frequency at the edge of the end of the first passband. Specify the value in either normalized frequency units or the absolute units you select in Frequency units.
Enter the frequency at the edge of the start of the stopband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
Enter the frequency at the edge of the end of the stopband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
Enter the frequency at the edge of the start of the second passband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
The parameters in this group let you specify the filter response in the passbands and stopbands.
Specify as Unconstrained or Constrained bands. You must have the DSP System Toolbox software to select Constrained bands. Selecting Constrained bands enables dialogs for both passbands and the stopband: Apass1, Apass2, and Astop. You cannot specify constraints for all three bands simultaneously.
Setting Magnitude constraints to Constrained bands enables the Wstop and Wpass options under Design options.
Specify the units for any parameter you provide in magnitude specifications. Select one of the following options from the drop-down list.
Linear — Specify the magnitude in linear units.
dB — Specify the magnitude in decibels (default).
Squared — Specify the magnitude in squared units.
Enter the filter ripple allowed in the first passband in the units you choose for Magnitude units, either linear or decibels.
Enter the filter attenuation in the stopband in the units you choose for Magnitude units, either linear or decibels
Enter the filter ripple allowed in the second passband in the units you choose for Magnitude units, either linear or decibels
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
Lists the design methods available for the frequency and magnitude specifications you entered. When you change the specifications for a filter, such as changing the impulse response, the methods available to design filters changes as well. The default IIR design method is usually Butterworth, and the default FIR method is equiripple.
Selecting this parameter directs the design to scale the filter coefficients to reduce the chances that the inputs or calculations in the filter overflow and exceed the representable range of the filter. Clearing this option removes the scaling. This parameter applies only to IIR filters.
Design Options
The options for each design are specific for each design method. This section does not present all of the available options for all designs and design methods. There are many more that you encounter as you select different design methods and filter specifications. The following options represent some of the most common ones available.
Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1).
Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 16 represents a reasonable trade between the accurate approximation to the ideal filter and the time to design the filter.
Valid when the Design method is equiripple and you have the DSP System Toolbox installed. Choose one of Linear, Minimum, or Maximum.
This option only applies when you have the DSP System Toolbox software and Order mode is Minimum.
Select Any (default), Even, or Odd. Selecting Even or Odd forces the minimum-order design to be an even or odd order.
Weight for the first passband.
Stopband weight.
Weight for the second passband.
Specifies that the resulting filter design matches either the passband or stopband or both bands when you select passband or stopband .
Valid only for IIR designs. Constrains the maximum pole radius. The default is 1. Reducing the max pole radius can produce a transfer function more resistant to quantization.
Valid only for IIR designs. The initial norm used in the optimization. The default initial norm is 2.
Specifies an initial estimate of the filter numerator coefficients. This may be useful in difficult optimization problems.
Specifies an initial estimate of the filter denominator coefficients. This may be useful in difficult optimization problems.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use direct-form structure, and IIR filters use direct-form II filters with SOS.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Parameters in this group enable you to specify your CIC filter format, such as the filter type and the differential delay.
Select whether your filter will be a decimator or an interpolator. Your choice determines the type of filter and the design methods and structures that are available to implement your filter. Selecting decimator or interpolator activates the Factor option. When you design an interpolator, you enable the Output Fs parameter.
When you design either a decimator or interpolator, the resulting filter is a CIC filter that decimates or interpolates your input signal.
Specify the differential delay of your CIC filter as an integer value greater than or equal to 1. The default value is 1. The differential delay changes the shape, number, and location of nulls in the filter response. Increasing the differential delay increases the sharpness of the nulls and the response between the nulls. In practice, differential delay values of 1 or 2 are the most common.
Specify the decimation or interpolation factor for your filter as an integer value greater than or equal to 1. The default value is 2.
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter output. When you provide an output sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available only when you design interpolators.
Enter the frequency at the end of the passband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
Specify the units for any parameter you provide in magnitude specifications. Select one of the following options from the drop-down list.
Linear — Specify the magnitude in linear units.
dB — Specify the magnitude in decibels (default).
Squared — Specify the magnitude in squared units.
Enter the filter attenuation in the stopband in the units you choose for Magnitude units, either linear or decibels.
Parameters in this group enable you to specify your filter format, such as the filter order mode and the filter type.
Select Minimum (the default) or Specify from the drop-down list. Selecting Specify enables the Order option (see the following sections) so you can enter the filter order.
Select Single-rate, Decimator, Interpolator, or Sample-rate converter. Your choice determines the type of filter as well as the design methods and structures that are available to implement your filter. By default, filterbuilder specifies single-rate filters.
Selecting Decimator or Interpolator activates the Decimation Factor or the Interpolation Factor options respectively.
Selecting Sample-rate converter activates both factors.
When you design either a decimator or an interpolator, the resulting filter is a bandpass filter that either decimates or interpolates your input signal.
Enter the filter order. This option is enabled only if Specify was selected for Order mode.
Enter the decimation factor. This option is enabled only if the Filter type is set to Decimator or Sample-rate converter. The default factor value is 2.
Enter the decimation factor. This option is enabled only if the Filter type is set to Interpolator or Sample-rate converter. The default factor value is 2.
Specify the number of sections in the CIC filter for which you are designing this compensator. Select the number of sections from the drop-down list or enter the number.
Specify the differential delay of your target CIC filter. The default value is 1. Most CIC filters use 1 or 2.
Frequency specifications
The parameters in this group allow you to specify your filter response curve.
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter output. When you provide an output sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available only when you design interpolators.
Enter the frequency at the end of the passband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
Enter the frequency at the start of the stopband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
The parameters in this group let you specify the filter response in the passbands and stopbands.
Specify the units for any parameter you provide in magnitude specifications. Select one of the following options from the drop-down list.
Linear — Specify the magnitude in linear units.
dB — Specify the magnitude in decibels (default).
Squared — Specify the magnitude in squared units.
Enter the filter ripple allowed in the passband in the units you choose for Magnitude units, either linear or decibels
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
Lists the design methods available for the frequency and magnitude specifications you entered. When you change the specifications for a filter, such as changing the impulse response, the methods available to design filters changes as well. The default IIR design method is usually Butterworth, and the default FIR method is equiripple.
Design Options
The options for each design are specific for each design method. This section does not present all of the available options for all designs and design methods. There are many more that you encounter as you select different design methods and filter specifications. The following options represent some of the most common ones available.
Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1).
Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 16 represents a reasonable trade between the accurate approximation to the ideal filter and the time to design the filter.
To design a filter that is minimum phase, select Minimum phase. Clearing the Minimum phase option removes the phase constraint—the resulting design is not minimum phase.
When you select this parameter, the design method determines and design the minimum order filter to meet your specifications. Some filters do not provide this parameter. Select Any, Even, or Odd from the drop-down list to direct the design to be any minimum order, or minimum even order, or minimum odd order.
Specifies that the resulting filter design matches either the passband or stopband or both bands when you select passband or stopband or both from the drop-down list.
Stopband shape lets you specify how the stopband changes with increasing frequency. Choose one of the following options:
Flat — Specifies that the stopband is flat. The attenuation does not change as the frequency increases.
Linear — Specifies that the stopband attenuation changes linearly as the frequency increases. Change the slope of the stopband by setting Stopband decay.
1/f — Specifies that the stopband attenuation changes exponentially as the frequency increases, where f is the frequency. Set the power (exponent) for the decay in Stopband decay.
When you set Stopband shape, Stopband decay specifies the amount of decay applied to the stopband. the following conditions apply to Stopband decay based on the value of Stopband Shape:
When you set Stopband shape to Flat, Stopband decay has no affect on the stopband.
When you set Stopband shape to Linear, enter the slope of the stopband in units of dB/rad/s. filterbuilder applies that slope to the stopband.
When you set Stopband shape to 1/f, enter a value for the exponent n in the relation (1/f)^{n} to define the stopband decay. filterbuilder applies the (1/f)^{n} relation to the stopband to result in an exponentially decreasing stopband attenuation.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use direct-form structure, and IIR filters use direct-form II filters with SOS.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Parameters in this group enable you to specify the type of comb filter and the number of peaks or notches.
Select Notch or Peak from the drop-down list. Notch creates a comb filter that attenuates a set of harmonically related frequencies. Peak creates a comb filter that amplifies a set of harmonically related frequencies.
Select Order or Number of Peaks/Notches from the drop-down menu.
Select Order to enter the desired filter order in the dialog box. The comb filter has notches or peaks at increments of 2/Order in normalized frequency units.
Select Number of Peaks or Number of Notches to specify the number of peaks or notches and the Shelving filter order
.
The Shelving filter order is a positive integer that determines the sharpness of the peaks or notches. Larger values result in sharper peaks or notches.
Parameters in this group enable you to specify the frequency constraints and frequency units.
Select Quality factor or Bandwidth.
Quality factor is the ratio of the center frequency of the peak or notch to the bandwidth calculated at the –3 dB point.
Bandwidth specifies the bandwidth of the peak or notch. By default the bandwidth is measured at the –3 dB point. For example, setting the bandwidth equal to 0.1 results in 3 dB frequencies at normalized frequencies 0.05 above and below the center frequency of the peak or notch.
Specify the frequency units. The default is normalized frequency. Choosing an option in Hz enables the Input Fs dialog box.
Specify the units for the magnitude specification and the gain at which the bandwidth is measured. This menu is disabled if you specify a filter order. Select one of the following magnitude units from the drop down list:
dB — Specify the magnitude in decibels (default).
Squared — Specify the magnitude in squared units.
Bandwidth gain — Specify the gain at which the bandwidth is measured. The default is –3 dB.
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off.
Parameters in this group enable you to specify your filter format, such as the impulse response and the filter order. Graphically, the filter specifications look similar to those shown in the following figure.
In the figure, regions between specification values such as Fpass (f_{1}) and Fstop (f_{3}) represent transition regions where the filter response is not explicitly defined.
Select Minimum (the default) or Specify from the drop-down list. Selecting Specify enables the Order option (see the following sections) so you can enter the filter order.
Select Single-rate, Decimator, Interpolator, or Sample-rate converter. Your choice determines the type of filter as well as the design methods and structures that are available to implement your filter. By default, filterbuilder specifies single-rate filters.
Selecting Decimator or Interpolator activates the Decimation Factor or the Interpolation Factor options respectively.
Selecting Sample-rate converter activates both factors.
When you design either a decimator or an interpolator, the resulting filter is a bandpass filter that either decimates or interpolates your input signal.
Enter the filter order. This option is enabled only if Specify was selected for Order mode.
Enter the decimation factor. This option is enabled only if the Filter type is set to Decimator or Sample-rate converter. The default factor value is 2.
Enter the decimation factor. This option is enabled only if the Filter type is set to Interpolator or Sample-rate converter. The default factor value is 2.
The parameters in this group allow you to specify your filter response curve.
This option is only available when you specify the order of the filter design. Supported options are Unconstrained and Passband edge and stopband edge.
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Enter the frequency at the end of the passband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
Enter the frequency at the start of the stopband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
The parameters in this group let you specify the filter response in the passbands and stopbands.
This option is only available when you specify the order of your filter design. The options for Magnitude constraints depend on the value of the Frequency constraints. If the value of Frequency constraints is Unconstrained, Magnitude constraints must be Unconstrained. If the value of Frequency constraints is Passband edge and stopband edge, Magnitude constraints can be Unconstrained, Passband ripple, or Stopband attenuation.
Specify the units for any parameter you provide in magnitude specifications. Select one of the following options from the drop-down list.
Linear — Specify the magnitude in linear units.
dB — Specify the magnitude in decibels (default).
Squared — Specify the magnitude in squared units.
Enter the filter ripple allowed in the passband in the units you choose for Magnitude units, either linear or decibels.
Enter the filter attenuation in the second stopband in the units you choose for Magnitude units, either linear or decibels.
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
Lists the design methods available for the frequency and magnitude specifications you entered. When you change the specifications for a filter, such as changing the impulse response, the methods available to design filters changes as well. The default IIR design method is usually Butterworth, and the default FIR method is equiripple.
Selecting this parameter directs the design to scale the filter coefficients to reduce the chances that the inputs or calculations in the filter overflow and exceed the representable range of the filter. Clearing this option removes the scaling. This parameter applies only to IIR filters.
Design Options
The options for each design are specific for each design method. This section does not present all of the available options for all designs and design methods. There are many more that you encounter as you select different design methods and filter specifications.
Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1).
Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 16 represents a reasonable trade between the accurate approximation to the ideal filter and the time to design the filter.
Passband weight. This option is only available for a specified-order design when Frequency constraints is equal to Passband edge and stopband edge and the Design method is Equiripple.
Stopband weight. This option is only available for a specified-order design when Frequency constraints is equal to Passband edge and stopband edge and the Design method is Equiripple.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use direct-form structure, and IIR filters use direct-form II filters with SOS.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Parameters in this group enable you to specify your filter format, such as the fractional delay and the filter order.
If you choose Specify for Order mode, enter your filter order in this field, or select the order from the drop-down list.filterbuilder designs a filter with the order you specify.
Specify a value between 0 and 1 samples for the filter fractional delay. The default value is 0.5 samples.
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Parameters in this group enable you to specify your filter type and order.
Select FIR or IIR from the drop-down list, where FIR is the default impulse response. When you choose an impulse response, the design methods and structures you can use to implement your filter change accordingly.
Select Minimum (the default) or Specify from the drop-down list. Selecting Specify enables the Order option (see the following sections) so you can enter the filter order.
Select Single-rate, Decimator, or Interpolator. By default, filterbuilder specifies single-rate filters.
When you design either a decimator or an interpolator, the resulting filter is a bandpass filter that decimates or interpolates your input by a factor of two.
Enter the filter order. This option is enabled only if Specify was selected for Order mode.
The parameters in this group allow you to specify your filter response curve. Graphically, the filter specifications for a halfband lowpass filter look similar to those shown in the following figure.
In the figure, the transition region lies between the end of the passband and the start of the stopband. The width is defined explicitly by the value of Transition width.
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Specify the width of the transition between the end of the passband and the edge of the stopband. Specify the value in normalized frequency units or the absolute units you select in Frequency units.
The parameters in this group let you specify the filter response in the passbands and stopbands.
Specify the units for any parameter you provide in magnitude specifications. Select one of the following options from the drop-down list.
Linear — Specify the magnitude in linear units.
dB — Specify the magnitude in decibels (default).
Enter the filter attenuation in the stopband in the units you choose for Magnitude units, either linear or decibels.
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
Lists the design methods available for the frequency and magnitude specifications you entered. For FIR halfband filters, the available design options are Equiripple and Kaiser window. For IIR halfband filters, the available design options are Butterworth, Elliptic, and IIR quasi-linear phase.
Design Options
The following design options are available for FIR halfband filters when the user specifies an equiripple design:
To design a filter that is minimum phase, select Minimum phase. Clearing the Minimum phase option removes the phase constraint—the resulting design is not minimum phase.
Stopband shape lets you specify how the stopband changes with increasing frequency. Choose one of the following options:
Flat — Specifies that the stopband is flat. The attenuation does not change as the frequency increases.
Linear — Specifies that the stopband attenuation changes linearly as the frequency increases. Change the slope of the stopband by setting Stopband decay.
1/f — Specifies that the stopband attenuation changes exponentially as the frequency increases, where f is the frequency. Set the power (exponent) for the decay in Stopband decay.
When you set Stopband shape, Stopband decay specifies the amount of decay applied to the stopband. the following conditions apply to Stopband decay based on the value of Stopband Shape:
When you set Stopband shape to Flat, Stopband decay has no affect on the stopband.
When you set Stopband shape to Linear, enter the slope of the stopband in units of dB/rad/s. filterbuilder applies that slope to the stopband.
When you set Stopband shape to 1/f, enter a value for the exponent n in the relation (1/f)^{n} to define the stopband decay. filterbuilder applies the (1/f)^{n} relation to the stopband to result in an exponentially decreasing stopband attenuation.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Parameters in this group enable you to specify your filter format, such as the impulse response and the filter order.
Select FIR or IIR from the drop-down list, where FIR is the default impulse response. When you choose an impulse response, the design methods and structures you can use to implement your filter change accordingly.
Select Minimum (the default) or Specify from the drop-down list. Selecting Specify enables the Order option so you can enter the filter order.
If your Impulse response is IIR, you can specify an equal order for the numerator and denominator, or different numerator and denominator orders. The default is equal orders. To specify a different denominator order, check the Denominator order box.
This option is only available if you have the DSP System Toolbox software. Select Single-rate, Decimator, Interpolator, or Sample-rate converter. Your choice determines the type of filter as well as the design methods and structures that are available to implement your filter. By default, filterbuilder specifies single-rate filters.
Selecting Decimator or Interpolator activates the Decimation Factor or the Interpolation Factor options respectively.
Selecting Sample-rate converter activates both factors.
When you design either a decimator or an interpolator, the resulting filter is a highpass filter that either decimates or interpolates your input signal.
Enter the filter order. This option is enabled only if Specify was selected for Order mode.
Enter the decimation factor. This option is enabled only if the Filter type is set to Decimator or Sample-rate converter. The default factor value is 2.
Enter the interpolation factor. This option is enabled only if the Filter type is set to Interpolator or Sample-rate converter. The default factor value is 2.
The parameters in this group allow you to specify your filter response curve. Graphically, the filter specifications look similar to those shown in the following figure.
In the figure, the region between specification values Fstop and Fpass represents the transition region where the filter response is not explicitly defined.
Select the filter features to use to define the frequency response characteristics. The list contains the following options, when available for the filter specifications.
Stopband edge and passband edge — Define the filter by specifying the frequencies for the edges for the stopband and passband.
Passband edge — Define the filter by specifying the frequency for the edge of the passband.
Stopband edge — Define the filter by specifying the frequency for the edges of the stopband.
Stopband edge and 3dB point — Define the filter by specifying the stopband edge frequency and the 3-dB down point (IIR designs).
3dB point and passband edge — Define the filter by specifying the 3-dB down point and passband edge frequency (IIR designs).
3dB point — Define the filter by specifying the frequency for the 3-dB point (IIR designs or maxflat FIR).
6dB point — Define the filter by specifying the frequency for the 6-dB point in the filter response (FIR designs).
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Enter the frequency at the of the passband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
Enter the frequency at the start of the stopband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
The parameters in this group let you specify the filter response in the passbands and stopbands.
Specify the units for any parameter you provide in magnitude specifications. Select one of the following options from the drop-down list.
Linear — Specify the magnitude in linear units.
dB — Specify the magnitude in decibels (default).
Squared — Specify the magnitude in squared units.
Enter the filter attenuation in the stopband in the units you choose for Magnitude units, either linear or decibels.
Enter the filter ripple allowed in the passband in the units you choose for Magnitude units, either linear or decibels.
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
Lists the design methods available for the frequency and magnitude specifications you entered. When you change the specifications for a filter, such as changing the impulse response, the methods available to design filters changes as well. The default IIR design method is usually Butterworth, and the default FIR method is equiripple.
Selecting this parameter directs the design to scale the filter coefficients to reduce the chances that the inputs or calculations in the filter overflow and exceed the representable range of the filter. Clearing this option removes the scaling. This parameter applies only to IIR filters.
Design Options
The options for each design are specific for each design method. This section does not present all of the available options for all designs and design methods. There are many more that you encounter as you select different design methods and filter specifications. The following options represent some of the most common ones available.
Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1).
Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 16 represents a reasonable trade between the accurate approximation to the ideal filter and the time to design the filter.
This option only applies when you have the DSP System Toolbox software and when the Design method is equiripple. Select one of Linear, Minimum, or Maximum.
Select Any (default), Even, or Odd. Selecting Even or Odd forces the minimum-order design to be an even or odd order.
Specifies that the resulting filter design matches either the passband or stopband when you select Passband or Stopband.
Stopband shape lets you specify how the stopband changes with increasing frequency. Choose one of the following options:
Flat — Specifies that the stopband is flat. The attenuation does not change as the frequency increases.
Linear — Specifies that the stopband attenuation changes linearly as the frequency increases. Change the slope of the stopband by setting Stopband decay.
1/f — Specifies that the stopband attenuation changes exponentially as the frequency increases, where f is the frequency. Set the power (exponent) for the decay in Stopband decay.
When you set Stopband shape, Stopband decay specifies the amount of decay applied to the stopband. the following conditions apply to Stopband decay based on the value of Stopband Shape:
When you set Stopband shape to Flat, Stopband decay has no affect on the stopband.
When you set Stopband shape to Linear, enter the slope of the stopband in units of dB/rad/s. filterbuilder applies that slope to the stopband.
When you set Stopband shape to 1/f, enter a value for the exponent n in the relation (1/f)^{n} to define the stopband decay. filterbuilder applies the (1/f)^{n} relation to the stopband to result in an exponentially decreasing stopband attenuation.
Passband weight. This option only applies when Impulse response is FIR and Order mode is Specify.
Stopband weight. This option only applies when Impulse response is FIR and Order mode is Specify.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use direct-form structure, and IIR filters use direct-form II filters with SOS.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Parameters in this group enable you to specify your filter format, such as the impulse response and the filter order.
Select FIR or IIR from the drop-down list, where FIR is the default impulse response. When you choose an impulse response, the design methods and structures you can use to implement your filter change accordingly.
This option is only available if you have the DSP System Toolbox software. Select either Minimum (the default) or Specify from the drop-down list. Selecting Specify enables the Order option (see the following sections) so you can enter the filter order.
This option is only available if you have the DSP System Toolbox software. Select Single-rate, Decimator, Interpolator, or Sample-rate converter. Your choice determines the type of filter as well as the design methods and structures that are available to implement your filter. By default, filterbuilder specifies single-rate filters.
Selecting Decimator or Interpolator activates the Decimation Factor or the Interpolation Factor options respectively.
Selecting Sample-rate converter activates both factors.
When you design either a decimator or an interpolator, the resulting filter is a bandpass filter that either decimates or interpolates your input signal.
Enter the filter order. This option is enabled only if Specify was selected for Order mode.
Enter the decimation factor. This option is enabled only if the Filter type is set to Decimator or Sample-rate converter. The default factor value is 2.
Enter the decimation factor. This option is enabled only if the Filter type is set to Interpolator or Sample-rate converter. The default factor value is 2.
The parameters in this group allow you to specify your filter response curve. Graphically, the filter specifications look similar to those shown in the following figure.
In the figure, the regions between 0 and f_{1} and between f_{2} and 1 represent the transition regions where the filter response is explicitly defined by the transition width.
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Specify the width of the transitions at the ends of the passband. Specify the value in normalized frequency units or the absolute units you select in Frequency units.
The parameters in this group let you specify the filter response in the passbands and stopbands.
Specify the units for any parameter you provide in magnitude specifications. Select one of the following options from the drop-down list.
Linear — Specify the magnitude in linear units.
dB — Specify the magnitude in decibels (default)
Squared — Specify the magnitude in squared units.
Enter the filter ripple allowed in the passband in the units you choose for Magnitude units, either linear or decibels.
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
Lists the design methods available for the frequency and magnitude specifications you entered. When you change the specifications for a filter, such as changing the impulse response, the methods available to design filters changes as well. The default IIR design method is usually Butterworth, and the default FIR method is equiripple.
Selecting this parameter directs the design to scale the filter coefficients to reduce the chances that the inputs or calculations in the filter overflow and exceed the representable range of the filter. Clearing this option removes the scaling. This parameter applies only to IIR filters.
Design Options
The options for each design are specific for each design method. This section does not present all of the available options for all designs and design methods. There are many more that you encounter as you select different design methods and filter specifications. The following options represent some of the most common ones available.
Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1).
Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 16 represents a reasonable trade between the accurate approximation to the ideal filter and the time to design the filter.
This option is only available in a minimum-order design. Specify whether to design a type 3 or a type 4 FIR filter. The filter type is defined as follows:
Type 3 — FIR filter with even order antisymmetric coefficients
Type 4 — FIR filter with odd order antisymmetric coefficients
Select 3 or 4 from the drop-down list.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use direct-form structure, and IIR filters use direct-form II filters with SOS.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Parameters in this group enable you to specify your filter format, such as the impulse response and the filter order.
Select Minimum (the default) or Specify from the drop-down list. Selecting Specify enables the Order option (see the following sections) so you can enter the filter order.
Select Lowpass or Highpass to design an inverse sinc lowpass or highpass filter.
Select Single-rate, Decimator, Interpolator, or Sample-rate converter. Your choice determines the type of filter as well as the design methods and structures that are available to implement your filter. By default, filterbuilder specifies single-rate filters.
Selecting Decimator or Interpolator activates the Decimation Factor or the Interpolation Factor options respectively.
Selecting Sample-rate converter activates both factors.
When you design either a decimator or an interpolator, the resulting filter is a bandpass filter that either decimates or interpolates your input signal.
Enter the filter order. This option is enabled only if Specify was selected for Order mode.
Enter the decimation factor. This option is enabled only if the Filter type is set to Decimator or Sample-rate converter. The default factor value is 2.
Enter the decimation factor. This option is enabled only if the Filter type is set to Interpolator or Sample-rate converter. The default factor value is 2.
The parameters in this group allow you to specify your filter response curve. Graphically, the filter specifications look similar to those shown in the following figure.
Regions between specification values such as Fpass and Fstop represent transition regions where the filter response is not explicitly defined.
This option is only available when you specify the filter order. The following options are available:
Passband and stopband edges — Define the filter by specifying the frequencies for the edges for the stop- and passbands.
Passband edge — Define the filter by specifying frequencies for the edges of the passband.
Stopband edge — Define the filter by specifying frequencies for the edges of the stopbands.
6dB point — The 6-dB point is the frequency for the point 6 dB point below the passband value.
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Enter the frequency at the end of the passband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
Enter the frequency at the start of the stopband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
The parameters in this group let you specify the filter response in the passbands and stopbands.
Specify the units for any parameter you provide in magnitude specifications. Select one of the following options from the drop-down list.
Linear — Specify the magnitude in linear units.
dB — Specify the magnitude in decibels (default)
Squared — Specify the magnitude in squared units.
Enter the filter ripple allowed in the passband in the units you choose for Magnitude units, either linear or decibels.
Enter the filter attenuation in the stopband in the units you choose for Magnitude units, either linear or decibels.
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
Lists the design methods available for the frequency and magnitude specifications you entered. When you change the specifications for a filter, such as changing the impulse response, the methods available to design filters changes as well. The default IIR design method is usually Butterworth, and the default FIR method is equiripple.
Design Options
The options for each design are specific for each design method. This section does not present all of the available options for all designs and design methods. There are many more that you encounter as you select different design methods and filter specifications. The following options represent some of the most common ones available.
Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1).
Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 16 represents a reasonable trade between the accurate approximation to the ideal filter and the time to design the filter.
Available options are Linear, Minimum, and Maximum.
Stopband shape lets you specify how the stopband changes with increasing frequency. Choose one of the following options;
Flat — Specifies that the stopband is flat. The attenuation does not change as the frequency increases.
Linear — Specifies that the stopband attenuation changes linearly as the frequency increases. Change the slope of the stopband by setting Stopband decay.
1/f — Specifies that the stopband attenuation changes exponentially as the frequency increases, where f is the frequency. Set the power (exponent) for the decay in Stopband decay.
When you set Stopband shape, Stopband decay specifies the amount of decay applied to the stopband. the following conditions apply to Stopband decay based on the value of Stopband Shape:
When you set Stopband shape to Flat, Stopband decay has no affect on the stopband.
When you set Stopband shape to Linear, enter the slope of the stopband in units of dB/rad/s. filterbuilder applies that slope to the stopband.
When you set Stopband shape to 1/f, enter a value for the exponent n in the relation (1/f)^{n} to define the stopband decay. filterbuilder applies the (1/f)^{n} relation to the stopband to result in an exponentially decreasing stopband attenuation.
A frequency dilation factor. The sinc frequency factor, C , parameterizes the passband magnitude response for a lowpass design through H(ω) = sinc(Cω)^(-P) and for a highpass design through H(ω) = sinc(C(1-ω))^(-P).
Negative power of passband magnitude response. The sinc power, P, parameterizes the passband magnitude response for a lowpass design through H(ω) = sinc(Cω)^(-P) and for a highpass design through H(ω) = sinc(C(1-ω))^(-P).
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use direct-form structure.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Parameters in this group enable you to specify your filter format, such as the impulse response and the filter order.
Select FIR or IIR from the drop-down list, where FIR is the default impulse response. When you choose an impulse response, the design methods and structures you can use to implement your filter change accordingly.
Select Minimum (the default) or Specify from the drop-down list. Selecting Specify enables the Order option (see the following sections) so you can enter the filter order.
If your Impulse response is IIR, you can specify an equal order for the numerator and denominator, or different numerator and denominator orders. The default is equal orders. To specify a different denominator order, check the Denominator order box.
This option is only available if you have the DSP System Toolbox. Select Single-rate, Decimator, Interpolator, or Sample-rate converter. Your choice determines the type of filter as well as the design methods and structures that are available to implement your filter. By default, filterbuilder specifies single-rate filters.
Selecting Decimator or Interpolator activates the Decimation Factor or the Interpolation Factor options respectively.
Selecting Sample-rate converter activates both factors.
When you design either a decimator or an interpolator, the resulting filter is a bandpass filter that either decimates or interpolates your input signal.
Enter the filter order. This option is enabled only if Specify was selected for Order mode.
Enter the decimation factor. This option is enabled only if the Filter type is set to Decimator or Sample-rate converter. The default factor value is 2.
Enter the decimation factor. This option is enabled only if the Filter type is set to Interpolator or Sample-rate converter. The default factor value is 2.
The parameters in this group allow you to specify your filter response curve. Graphically, the filter specifications look similar to the one shown in the following figure.
In the figure, regions between specification values such as F_{pass} and F_{stop} represent transition regions where the filter response is not explicitly defined.
Select the filter features to use to define the frequency response characteristics. The list contains the following options, when available for the filter specifications.
Passband and stopband edge — Define the filter by specifying the frequencies for the edge of the stopband and passband.
Passband edge — Define the filter by specifying the frequency for the edge of the passband.
Stopband edge — Define the filter by specifying the frequency for the edges of the stopband.
Passband edge and 3dB point — Define the filter by specifying the passband edge frequency and the 3-dB down point (IIR designs).
3dB point and stopband edge — Define the filter by specifying the 3-dB down point and stopband edge frequency (IIR designs).
3dB point — Define the filter by specifying the frequency for the 3-dB point (IIR designs or maxflat FIR).
6dB point — Define the filter by specifying the frequency for the 6-dB point in the filter response (FIR designs).
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Enter the frequency at the of the passband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
Enter the frequency at the start of the stopband. Specify the value in either normalized frequency units or the absolute units you select Frequency units.
The parameters in this group let you specify the filter response in the passbands and stopbands.
Specify the units for any parameter you provide in magnitude specifications. Select one of the following options from the drop-down list.
Linear — Specify the magnitude in linear units.
dB — Specify the magnitude in decibels (default)
Squared — Specify the magnitude in squared units.
Enter the filter ripple allowed in the passband in the units you choose for Magnitude units, either linear or decibels.
Enter the filter attenuation in the stopband in the units you choose for Magnitude units, either linear or decibels.
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
Lists the design methods available for the frequency and magnitude specifications you entered. When you change the specifications for a filter, such as changing the impulse response, the methods available to design filters changes as well. The default IIR design method is usually Butterworth, and the default FIR method is equiripple.
Selecting this parameter directs the design to scale the filter coefficients to reduce the chances that the inputs or calculations in the filter overflow and exceed the representable range of the filter. Clearing this option removes the scaling. This parameter applies only to IIR filters.
Design Options
The options for each design are specific for each design method. This section does not present all of the available options for all designs and design methods. There are many more that you encounter as you select different design methods and filter specifications. The following options represent some of the most common ones available.
Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1).
Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 16 represents a reasonable trade between the accurate approximation to the ideal filter and the time to design the filter.
This option only applies when you have the DSP System Toolbox software and when the Design method is equiripple. Select one of Linear, Minimum, or Maximum.
Select Any (default), Even, or Odd. Selecting Even or Odd forces the minimum-order design to be an even or odd order.
Specifies that the resulting filter design matches either the passband or stopband when you select Passband or Stopband.
Stopband shape lets you specify how the stopband changes with increasing frequency. Choose one of the following options:
Flat — Specifies that the stopband is flat. The attenuation does not change as the frequency increases.
Linear — Specifies that the stopband attenuation changes linearly as the frequency increases. Change the slope of the stopband by setting Stopband decay.
1/f — Specifies that the stopband attenuation changes exponentially as the frequency increases, where f is the frequency. Set the power (exponent) for the decay in Stopband decay.
When you set Stopband shape, Stopband decay specifies the amount of decay applied to the stopband. the following conditions apply to Stopband decay based on the value of Stopband Shape:
When you set Stopband shape to Flat, Stopband decay has no affect on the stopband.
When you set Stopband shape to Linear, enter the slope of the stopband in units of dB/rad/s. filterbuilder applies that slope to the stopband.
When you set Stopband shape to 1/f, enter a value for the exponent n in the relation (1/f)^{n} to define the stopband decay. filterbuilder applies the (1/f)^{n} relation to the stopband to result in an exponentially decreasing stopband attenuation.
Passband weight. This option only applies when Impulse response is FIR and Order mode is Specify.
Stopband weight. This option only applies when Impulse response is FIR and Order mode is Specify.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use direct-form structure, and IIR filters use direct-form II filters with SOS.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
See Peak/Notch Filter Design Dialog Box — Main Pane.
Parameters in this group enable you to specify your filter format, such as the impulse response and the filter order.
Specifies the location of the center of the transition region between the passband and the stopband. The center of the transition region, bw, is calculated using the value for Band:
bw = Fs/(2*Band).
Select FIR or IIR from the drop-down list, where FIR is the default impulse response. When you choose an impulse response, the design methods and structures you can use to implement your filter change accordingly.
Select Minimum (the default) or Specify from the drop-down list. Selecting Specify enables the Order option (see the following sections) so you can enter the filter order.
Select Single-rate, Decimator, Interpolator, or Sample-rate converter. Your choice determines the type of filter as well as the design methods and structures that are available to implement your filter. By default, filterbuilder specifies single-rate filters.
Selecting Decimator or Interpolator activates the Decimation Factor or the Interpolation Factor options respectively.
Selecting Sample-rate converter activates both factors.
When you design either a decimator or an interpolator, the resulting filter is a bandpass filter that either decimates or interpolates your input signal.
Enter the filter order. This option is enabled only if Specify was selected for Order mode.
Enter the decimation factor. This option is enabled only if the Filter type is set to Decimator or Sample-rate converter. The default factor value is 2.
Enter the decimation factor. This option is enabled only if the Filter type is set to Interpolator or Sample-rate converter. The default factor value is 2.
The parameters in this group allow you to specify your filter response curve. Graphically, the filter specifications look similar to those shown in the following figure.
In the figure, BW is the width of the transition region and Band determines the location of the center of the region.
Select the filter features to use to define the frequency response characteristics. The list contains the following options, when available for the filter specifications.
Passband and stopband edges — Define the filter by specifying the frequencies for the edges for the stopbands and passbands.
Passband edges — Define the filter by specifying frequencies for the edges of the passband.
Stopband edges — Define the filter by specifying frequencies for the edges of the stopbands.
3 dB points — Define the filter response by specifying the locations of the 3 dB points. The 3 dB point is the frequency for the point 3 dB point below the passband value.
3 dB points and passband width — Define the filter by specifying frequencies for the 3 dB points in the filter response and the width of the passband.
3 dB points and stopband widths — Define the filter by specifying frequencies for the 3 dB points in the filter response and the width of the stopband.
Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0–1) to enter frequencies in normalized form. This behavior is the default. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz. Selecting one of the unit options enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Specify the width of the transition between the end of the passband and the edge of the stopband. Specify the value in normalized frequency units or the absolute units you select in Frequency units.
The parameters in this group let you specify the filter response in the passbands and stopbands.
Specify the units for any parameter you provide in magnitude specifications. Select one of the following options from the drop-down list.
Linear — Specify the magnitude in linear units.
dB — Specify the magnitude in decibels (default)
Squared — Specify the magnitude in squared units.
Enter the filter attenuation in the stopband in the units you choose for Magnitude units, either linear or decibels.
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
Lists the design methods available for the frequency and magnitude specifications you entered. When you change the specifications for a filter, such as changing the impulse response, the methods available to design filters changes as well. The default IIR design method is usually Butterworth, and the default FIR method is equiripple.
Selecting this parameter directs the design to scale the filter coefficients to reduce the chances that the inputs or calculations in the filter overflow and exceed the representable range of the filter. Clearing this option removes the scaling. This parameter applies only to IIR filters.
Design Options
The options for each design are specific for each design method. This section does not present all of the available options for all designs and design methods. There are many more that you encounter as you select different design methods and filter specifications. The following options represent some of the most common ones available.
Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1).
Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 16 represents a reasonable trade between the accurate approximation to the ideal filter and the time to design the filter.
To design a filter that is minimum phase, select Minimum phase. Clearing the Minimum phase option removes the phase constraint—the resulting design is not minimum phase.
When you select this parameter, the design method determines and designs the minimum order filter to meet your specifications. Some filters do not provide this parameter. Select Any, Even, or Odd from the drop-down list to direct the design to be any minimum order, or minimum even order, or minimum odd order.
Specifies that the resulting filter design matches either the passband or stopband or both bands when you select passband or stopband or both from the drop-down list.
Stopband shape lets you specify how the stopband changes with increasing frequency. Choose one of the following options:
Flat — Specifies that the stopband is flat. The attenuation does not change as the frequency increases.
Linear — Specifies that the stopband attenuation changes linearly as the frequency increases. Change the slope of the stopband by setting Stopband decay.
1/f — Specifies that the stopband attenuation changes exponentially as the frequency increases, where f is the frequency. Set the power (exponent) for the decay in Stopband decay.
When you set Stopband shape, Stopband decay specifies the amount of decay applied to the stopband. the following conditions apply to Stopband decay based on the value of Stopband Shape:
When you set Stopband shape to Flat, Stopband decay has no affect on the stopband.
When you set Stopband shape to Linear, enter the slope of the stopband in units of dB/rad/s. filterbuilder applies that slope to the stopband.
When you set Stopband shape to 1/f, enter a value for the exponent n in the relation (1/f)^{n} to define the stopband decay. filterbuilder applies the (1/f)^{n} relation to the stopband to result in an exponentially decreasing stopband attenuation.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use direct-form structure, and IIR filters use direct-form II filters with SOS.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Specify filter order. Possible values are: 4, 6, 8, 10.
Specify the number of bands per octave. Possible values are: 1, 3, 6, 12, 24.
Specify frequency units as Hz or kHz.
Specify the input sampling frequency in the frequency units specified previously.
Select from the drop-down list of available center frequency values.
Specify filter structure. Choose from:
Direct-form I SOS
Direct-form II SOS
Direct-form I transposed SOS
Direct-form II transposed SOS
Selecting this check box gives you the choice of using a system object to implement the filter. By default, the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Select Minimum to design a minimum order filter that meets the design specifications, or Specify to enter a specific filter order. The order mode also affects the possible frequency constraints, which in turn limit the gain specifications. For example, if you specify a Minimum order filter, the available frequency constraints are:
Center frequency, bandwidth, passband width
Center frequency, bandwidth, stopband width
If you select Specify, the available frequency constraints are:
Center frequency, bandwidth
Center frequency, quality factor
Shelf type, cutoff frequency, quality factor
Shelf type, cutoff frequency, shelf slope parameter
Low frequency, high frequency
This parameter is enabled only if the Order mode is set to Specify. Enter the filter order in this text box.
Depending on the filter order, the possible frequency constraints change. Once you choose the frequency constraints, the input boxes in this area change to reflect the selection.
Select the specification to represent the frequency constraints. The following options are available:
Center frequency, bandwidth, passband width (available for minimum order only)
Center frequency, bandwidth, stopband width (available for minimum order only)
Center frequency, bandwidth (available for a specified order only)
Center frequency, quality factor (available for a specified order only)
Shelf type, cutoff frequency, quality factor (available for a specified order only)
Shelf type, cutoff frequency, shelf slope parameter (available for a specified order only)
Low frequency, high frequency (available for a specified order only)
Select the frequency units from the available drop down list (Normalized, Hz, kHz, MHz, GHz). If Normalized is selected, then the Input Fs box is disabled for input.
Enter the input sampling frequency. This input box is disabled for input if Normalized is selected in the Frequency units input box.
Enter the center frequency in the units specified by the value in Frequency units.
The bandwidth determines the frequency points at which the filter magnitude is attenuated by the value specified as the Bandwidth gain in the Gain specifications section. By default, the Bandwidth gain defaults to db(sqrt(.5)), or –3 dB relative to the center frequency. The Bandwidth property only applies when the Frequency constraints are: Center frequency, bandwidth, passband width, Center frequency, bandwidth, stopband width, or Center frequency, bandwidth.
The passband width determines the frequency points at which the filter magnitude is attenuated by the value specified as the Passband gain in the Gain specifications section. This option is enabled only if the filter is of minimum order, and the frequency constraint selected is Center frequency, bandwidth, passband width.
The stopband width determines the frequency points at which the filter magnitude is attenuated by the value specified as the Stopband gain in the Gain specifications section. This option is enabled only if the filter is of minimum order, and the frequency constraint selected is Center frequency, bandwidth, stopband width.
Enter the low frequency cutoff. This option is enabled only if the filter order is user specified and the frequency constraint selected is Low frequency, high frequency. The filter magnitude is attenuated by the amount specified in Bandwidth gain.
Enter the high frequency cutoff. This option is enabled only if the filter order is user specified and the frequency constraint selected is Low frequency, high frequency. The filter magnitude is attenuated by the amount specified in Bandwidth gain.
Depending on the filter order and frequency constraints, the possible gain constraints change. Also, once you choose the gain constraints the input boxes in this area change to reflect the selection.
Select the specification array to represent gain constraints, and remember that not all of these options are available for all configurations. The following is a list of all available options:
Reference, center frequency, bandwidth, passband
Reference, center frequency, bandwidth, stopband
Reference, center frequency, bandwidth, passband, stopband
Reference, center frequency, bandwidth
Specify the gain units either dB or squared. These units are used for all gain specifications in the dialog box.
The reference gain determines the level to which the filter magnitude attenuates in Gain units. The reference gain is a floor gain for the filter magnitude response. For example, you may use the reference gain together with the Center frequency gain to leave certain frequencies unattenuated (reference gain of 0 dB) while boosting other frequencies.
Specifies the gain in Gain units at which the bandwidth is defined. This property applies only when the Frequency constraints specification contains a bandwidth parameter, or is Low frequency, high frequency.
Specify the center frequency in Gain units
The passband gain determines the level in Gain units at which the passband is defined. The passband is determined either by the Passband width value, or the Low frequency and High frequency values in the Frequency specifications section.
The stopband gain is the level in Gain units at which the stopband is defined. This property applies only when the Order mode is minimum and the Frequency constraints are Center frequency, bandwidth, stopband width.
The boost/cut gain applies only when the designing a shelving filter. Shelving filters include the Shelf type parameter in the Frequency constraints specification. The gain in the passband of the shelving filter is increased by Boost/cut gain dB from a floor gain of 0 dB.
Select filter structure. The possible choices are:
Direct-form I SOS
Direct-form II SOS
Direct-form I transposed SOS
Direct-form II transposed SOS
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
In this area you can specify whether you want to design a peaking filter or a notching filter, as well as the order of the filter.
This group of parameters allows you to specify frequency constraints and units.
Select the frequency constraints for filter specification. There are two choices as follows:
Center frequency and quality factor
Center frequency and bandwidth
The frequency units are normalized by default. If you specify units other than normalized, filterbuilder assumes that you wish to specify an input sampling frequency, and enables this input box. The choice of frequency units are: Normalized (0 to 1), Hz, kHz, MHz, GHz.
This input box is enabled if Frequency units other than Normalized (0 to 1) are specified. Enter the input sampling frequency.
Enter the center frequency in the units you specified in Frequency units.
This input box is enabled only when Center frequency and quality factor is chosen for the Frequency Constraints. Enter the quality factor.
This input box is enabled only when Center frequency and bandwidth is chosen for the Frequency Constraints. Enter the bandwidth.
This group of parameters allows you to specify the magnitude constraints, as well as their values and units.
Depending on the choice of constraints, the other input boxes are enabled or disabled. Select from four magnitude constraints available:
Unconstrained
Passband ripple
Stopband attenuation
Passband ripple and stopband attenuation
Select the magnitude units: either dB or squared.
This input box is enabled if the magnitude constraints selected are Passband ripple or Passband ripple and stopband attenuation. Enter the passband ripple.
This input box is enabled if the magnitude constraints selected are Stopband attenuation or Passband ripple and stopband attenuation. Enter the stopband attenuation.
The parameters in this group allow you to specify the design method and structure that filterbuilder uses to implement your filter.
Lists all design methods available for the frequency and magnitude specifications you entered. When you change the specifications for a filter the methods available to design filters changes as well.
Selecting this parameter directs the design to scale the filter coefficients to reduce the chances that the inputs or calculations in the filter overflow and exceed the representable range of the filter. Clearing this option removes the scaling. This parameter applies only to IIR filters.
Lists all available filter structures for the filter specifications and design method you select. The typical options are:
Direct-form I SOS
Direct-form II SOS
Direct-form I transposed SOS
Direct-form II transposed SOS
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.
Parameters in this group enable you to specify the shape and length of the filter.
Select the shape of the impulse response from the following options:
Raised Cosine
Square Root Raised Cosine
Gaussian
This specification is only available for raised cosine and square root raised cosine filters. For these filters, select one of the following options:
Minimum— This option will result in the minimum-length filter satisfying the user-specified Frequency specifications.
Specify order—This option allows the user to construct a raised cosine or square root cosine filter of a specified order by entering an even number in the Order input box. The length of the impulse response will be Order+1 .
Specify symbols—This option enables the user to specify the length of the impulse response in an alternative manner. If Specify symbols is chosen, the Order input box changes to the Number of symbols input box.
Specify the oversampling factor. Increasing the oversampling factor guards against aliasing and improves the FIR filter approximation to the ideal frequency response. If Order is specified in Number of symbols, the filter length will be Number of symbols*Samples per symbol+1. The product Number of symbols*Samples per symbol must be an even number.
If a Gaussian filter is specified, the filter length must be specified in Number of symbols and Samples per symbol. The product Number of symbols*Samples per symbol must be an even number. The filter length will be Number of symbols*Samples per symbol+1.
This option is only available if you have the DSP System Toolbox software. Choose Single rate, Decimator, Interpolator, or Sample-rate converter. If you select Decimator or Interpolator, the decimation and interpolation factors default to the value of the Samples per symbol. If you select Sample-rate converter, the interpolation factor defaults to Samples per symbol and the decimation factor defaults to 3.
Parameters in this group enable you to specify the frequency response of the filter. For raised cosine and square root raised cosine filters, the frequency specifications include:
The rolloff factor takes values in the range [0,1]. The smaller the rolloff factor, the steeper the transition in the stopband.
The frequency units are normalized by default. If you specify units other than normalized, filterbuilder assumes that you wish to specify an input sampling frequency, and enables this input box. The choice of frequency units are: Normalized (0 to 1), Hz, kHz, MHz, GHz
For a Gaussian pulse shape, the available frequency specifications are:
This option allows the user to specify the width of the Gaussian filter. Note that this is independent of the length of the filter. The bandwidth-time product (BT) must be a positive real number. Smaller values of the bandwidth-time product result in larger pulse widths in time and steeper stopband transitions in the frequency response.
The frequency units are normalized by default. If you specify units other than normalized, filterbuilder assumes that you wish to specify an input sampling frequency, and enables this input box. The choice of frequency units are: Normalized (0 to 1), Hz, kHz, MHz, GHz
If the Order mode is specified as Minimum, the Magnitude units may be selected from:
dB—Specify the magnitude in decibels (default).
Linear—Specify the magnitude in linear units.
The only Design method available for FIR pulse-shaping filters is the Window method.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use direct-form structure.
Selecting this check box gives you the choice of using a system object to implement the filter. By default the check box is turned off. When the current design method or structure is not supported by a system object filter, then this check box is disabled.