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filterBuilder

Interactive filter design

Syntax

filterBuilder(h)
filterBuilder('response')

Description

filterBuilder starts a interactive 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.

For more information on how to use filterBuilder, see Filter Builder 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 using fdesign.

    Note

    You must have the DSP System Toolbox software to create and import filter System objects.

  • Enter filterBuilder('response') to replace response with a response method from the following table. MATLAB opens a filter design dialog that corresponds to the specified response.

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 MethodDescription of Resulting Filter DesignFilter Object
arbgrpdelayArbitrary group delay filter designfdesign.arbgrpdelay
arbmagArbitrary magnitude filter designfdesign.arbmag
arbmagnphaseArbitrary response filter (magnitude and phase)fdesign.arbmagnphase
audioweightingAudio weighting filterfdesign.audioweighting
bandpass or bpBandpass filterfdesign.bandpass
bandstop or bsBandstop filterfdesign.bandstop
cicCIC filterfdesign.decimator(M,'cic',...) or fdesign.interpolator(L,'cic',...)
See fdesign.decimator and fdesign.interpolator
ciccompCIC compensatorfdesign.ciccomp
combComb filterfdesign.comb
diffDifferentiator filterfdesign.differentiator
fracdelayFractional delay filterfdesign.fracdelay
halfband or hbHalfband filterfdesign.halfband
highpass or hpHighpass filterfdesign.highpass
hilbHilbert filterfdesign.hilbert
isinc,
isinclp, or
isinchp
Inverse sinc lowpass or highpass filterfdesign.isinclp and
fdesign.isinchp
lowpass or lpLowpass filter (default)fdesign.lowpass
notchNotch filterfdesign.notch
nyquistNyquist filterfdesign.nyquist
octaveOctave filterfdesign.octave
parameqParametric equalizer filterfdesign.parameq
peakPeak filterfdesign.peak

Note

Because they do not change the filter structure, the magnitude specifications and design method are tunable when using filterBuilder.

Filter Builder Design Panes

Main Design Pane

The main pane of Filter Builder 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 Filter Builder 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.

Data Types Pane

The second tab in the Filter Builder 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 EntryEffect on the Filter
Double precisionAll 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 precisionAll filtering operations and coefficients use single-precision floating-point representations and math.
Fixed pointThis entry 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.

When you select Use a System object to implement filter check box in the Main pane, the Data Types pane appears as below:

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.

Input signal

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.

Coefficients

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.

Section Input

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.

Section Output

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.

State

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).

Product

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.

Filter internals

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.

Signed

Selecting this option directs the filter to use signed representations for the filter coefficients.

Word length

Sets the word length for the associated filter parameter in bits.

Fraction length

Sets the fraction length for the associate filter parameter in bits.

Accum

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.

Output

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.

Fixed-point operational parameters

Parameters in this group control how the filter rounds fixed-point values and how it treats values that overflow.

Rounding mode

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.

Overflow mode

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.

Cast before sum

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.

Code Generation Pane

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.

HDL

For more information on this option, see Opening the Filter Design HDL Coder UI from the Filter Builder (Filter Design HDL Coder).

MATLAB

Generate MATLAB code based on filter specifications

  • Generate function that returns your filter as an output

    Selecting this option generates a function that designs a filter object using fdesign.

  • 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. The data type of the filter output is set according to the data type settings in the Data Types pane.

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.

Simulink Model

Generate Simulink blocks and subsystems from your designed filters

When you click Generate Model, the filter builder generates Simulink blocks and subsystems from your designed filters.

Clicking on the Generate Model button opens the Export to Simulink dialog box.

  • Block Name — The name for the new subsystem block, set to Filter by default.

  • DestinationCurrent 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 at the location specified in User Defined.

  • Overwrite generated 'Filter' block — Overwrites an existing block with the name specified in Block Name. Clear this check box to create a new block with the same name.

  • Build model using basic elements — Builds the model using only basic blocks.

  • Optimize for zero gains — Removes all zero-gain blocks from the model.

  • Optimize for unity gains — Replaces all unity gains with direct connections.

  • Optimize for negative gains — Removes all negative unity gain blocks, and changes sign at the nearest summation block.

  • Optimize delay chains — Replaces delay chains made up of n unit delays with a single delay by n.

  • Optimize for unity scale values — 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) — The block treats each column of the input as a separate channel.

    • Elements as channels (sample based) — The block treats each element of the input as a separate channel.

    For more information about sample-based and frame-based processing, see Sample- and Frame-Based Concepts (DSP System Toolbox).

  • Realize Model — Builds the model with the set parameters.

When the Use a System object to implement filter check box is selected in the Main pane, the Generate Model button in the Simulink model panel is disabled under the following conditions:

  • Select Filter response as Comb and Arithmetic on the Data Types pane as Fixed point.

  • Select Filter response as Arbitrary Response, Impulse response as IIR, set Specify response as to either Magnitudes and phases or Frequency response, and Arithmetic on the Data Types pane as Fixed point.

These settings design a dsp.IIRFilter System object™ with fixed point arithmetic. Generating a Simulink model for fixed point dsp.IIRFilter object is not supported.

Filter Responses

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.

Arbitrary Response Filter Design — Main Pane

 Filter specifications

 Response Specification

 Band Properties

 Algorithm

 Filter implementation

Audio Weighting Filter Design — Main Pane

 Filter specifications

 Algorithm

 Filter implementation

Bandpass Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Bandstop Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

CIC Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

CIC Compensator Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Comb Filter Design —Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Differentiator Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Fractional Delay Design — Main Pane

 Frequency specifications

Halfband Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Highpass Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Hilbert Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Inverse Sinc Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Lowpass Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Nyquist Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Octave Filter Design — Main Pane

 Filter specifications

 Algorithm

 Filter implementation

Parametric Equalizer Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Gain specifications

 Algorithm

 Filter implementation

Peak/Notch Filter Design — Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Pulse-shaping Filter Design —Main Pane

 Filter specifications

 Frequency specifications

 Magnitude specifications

 Algorithm

 Filter implementation

Introduced in R2009a

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