Filter Design Toolbox™

dfilt.scalar - Discrete-time, scalar filter

Syntax

Refer to dfilt.scalar in Signal Processing Toolbox™ documentation.

Description

dfilt.scalar(g) returns a discrete-time, scalar filter object with gain g, where g is a scalar.

Make this filter a fixed-point or single-precision filter by changing the value of the Arithmetic property for the filter hd as follows:

To change to single-precision filtering, enter
```
set(hd,'arithmetic','single');
```
To change to fixed-point filtering, enter
```
set(hd,'arithmetic','fixed');
```

For more information about the property Arithmetic, refer to Arithmetic.

dfilt.scalar returns a default, discrete-time scalar gain filter object hd, with gain 1.

Properties

In this table you see the properties associated with the scalar implementation of dfilt objects.

Note The table lists all the properties that a filter can have. Many of the properties are dynamic, meaning they exist only in response to the settings of other properties. You might not see all of the listed properties all the time. To view all the properties for a filter at any time, use

get(hd)

where hd is a filter.

For further information about the properties of this filter or any dfilt object, refer to Fixed-Point Filter Properties.

Property Name	Brief Description
`Arithmetic`	Defines the arithmetic the filter uses. Gives you the options `double`, `single`, and `fixed`. In short, this property defines the operating mode for your filter.
`CastBeforeSum`	Specifies whether to cast numeric data to the appropriate accumulator format (as shown in the signal flow diagrams) before performing sum operations.
`CoeffAutoScale`	Specifies whether the filter automatically chooses the proper fraction length to represent filter coefficients without overflowing. Turning this off by setting the value to `false` enables you to change the `CoeffFracLength` property to specify the precision used.
`CoeffFracLength`	Set the fraction length the filter uses to interpret coefficients. `CoeffFracLength` is always available, but it is read-only until you set `CoeffAutoScale` to `false`.
`CoeffWordLength`	Specifies the word length to apply to filter coefficients.
`FilterStructure`	Describes the signal flow for the filter object, including all of the active elements that perform operations during filtering — gains, delays, sums, products, and input/output.
`Gain`	Returns the gain for the scalar filter. Scalar filters do not alter the input data except by adding gain.
`InputFracLength`	Specifies the fraction length the filter uses to interpret input data.
`InputWordLength`	Specifies the word length applied to interpret input data.
`OutputFracLength`	Determines how the filter interprets the filter output data. You can change the value of `OutputFracLength` when you set `OutputMode` to `SpecifyPrecision`.
`OutputMode`	Sets the mode the filter uses to scale the filtered data for output. You have the following choices: `AvoidOverflow` — directs the filter to set the output data word length and fraction length to avoid causing the data to overflow. `BestPrecision` — directs the filter to set the output data word length and fraction length to maximize the precision in the output data. `SpecifyPrecision` — lets you set the word and fraction lengths used by the output data from filtering.
`OutputWordLength`	Determines the word length used for the output data.
`OverflowMode`	Sets the mode used to respond to overflow conditions in fixed-point arithmetic. Choose from either `saturate` (limit the output to the largest positive or negative representable value) or `wrap` (set overflowing values to the nearest representable value using modular arithmetic). The choice you make affects only the accumulator and output arithmetic. Coefficient and input arithmetic always saturates. Finally, products never overflow — they maintain full precision.
`PersistentMemory`	Specifies whether to reset the filter states and memory before each filtering operation. Lets you decide whether your filter retains states from previous filtering runs. `False` is the default setting.
`RoundMode`	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). `convergent` — Round up to the next allowable quantized value. `ceil` — Round to the nearest allowable quantized value. Numbers that are exactly halfway between the two nearest allowable quantized values are rounded up only if the least significant bit (after rounding) would be set to `1`. `fix` — Round negative numbers up and positive numbers down to the next allowable quantized value. `floor` — Round down to the next allowable quantized value. `round` — Round to the nearest allowable quantized value. Numbers that are halfway between the two nearest allowable quantized values are rounded up. The choice you make affects only the accumulator and output arithmetic. Coefficient and input arithmetic always round. Finally, products never overflow — they maintain full precision.
`Signed`	Specifies whether the filter uses signed or unsigned fixed-point coefficients. Only coefficients reflect this property setting.
`States`	This property contains the filter states before, during, and after filter operations. States act as filter memory between filtering runs or sessions. The states use `fi` objects, with the associated properties from those objects. For details, refer to `filtstates` in Signal Processing Toolbox documentation or in the Help system.

Example

Create a direct-form I filter object hd_filt and a scalar object with a gain of 3 hd_gain and cascade them together.

b = [0.3 0.6 0.3];
a = [1 0 0.2];
hd_filt = dfilt.df1(b,a)
hd_gain = dfilt.scalar(3)
hd=cascade(hd_gain,hd_filt)
fvtool(hd_filt,hd_gain,hd)
hd_filt = 
         FilterStructure: 'direct-form I'
              Arithmetic: 'double'
               Numerator: [0.3000 0.6000 0.3000]
             Denominator: [1 0 0.2000]
        PersistentMemory: false
                  States: [4x1 double]

hd_gain = 
         FilterStructure: 'Scalar'
              Arithmetic: 'double'
                    Gain: 3
        PersistentMemory: false
                  States: []
hd = 
         FilterStructure: Cascade
              Section(1): Scalar
              Section(2): Direct Form I
        PersistentMemory: false

To view the sections of the cascaded filter, use

hd.section(1)
 
ans = 
         FilterStructure: 'Scalar'
              Arithmetic: 'double'
                    Gain: 3
        PersistentMemory: false
                  States: []

and

hd.section(2)
 
ans = 
         FilterStructure: 'Direct Form I'
              Arithmetic: 'double'
               Numerator: [0.3000 0.6000 0.3000]
             Denominator: [1 0 0.2000]
        PersistentMemory: false
                  States: [4x1 double]

dfilt.scalar - Discrete-time, scalar filter

Syntax

Description

Properties

Example

See Also