toMultirate

Create multirate filter System object from digital FIR filter object

Since R2025a

Syntax

multiFiltObj = toMultirate(digiFiltObj,Name=Value)

Description

multiFiltObj = toMultirate(digiFiltObj,Name=Value) creates a multirate FIR filter System object™ from the input digitalFilter object based on the properties you specify using one or more name-value arguments. For example, multiFiltObj = toMultirate(digitFiltObj,InterpolationFactor=7,DecimationFactor=3) creates a dsp.FIRRateConverter object with an interpolation factor of 7 and a decimation factor of 3 using the filter coefficients from the digiFiltObj object.

Examples

Convert Lowpass Digital FIR Filter Object Into FIR Rate Converter Object

Design a lowpass digital FIR filter object with these design specifications using the designfilt function:

• Filter order of 22

• Passband frequency of 100 Hz

• Stopband frequency of 275 Hz

• Sample rate of 1000 Hz

• Least-squares design method

designedFilter = designfilt('lowpassfir', ...
    'FilterOrder',22,'PassbandFrequency',100, ...
    'StopbandFrequency',275,'SampleRate',1e3, ...
    'DesignMethod','ls')

designedFilter = 
 digitalFilter with properties:

   Coefficients:
            Numerator: [-9.9314e-05 -0.0016 -0.0031 0.0015 0.0131 0.0136 -0.0166 -0.0547 -0.0286 0.1064 0.2853 0.3693 0.2853 0.1064 -0.0286 -0.0547 -0.0166 0.0136 0.0131 0.0015 -0.0031 -0.0016 -9.9314e-05]
          Denominator: 1

   Specifications:
    FrequencyResponse: 'lowpass'
      ImpulseResponse: 'fir'
           SampleRate: 1000
    StopbandFrequency: 275
    PassbandFrequency: 100
          FilterOrder: 22
         DesignMethod: 'ls'

 Use filterAnalyzer to visualize filter
 Use designfilt to edit filter
 Use filter to filter data

Convert the designed digitalFilter object into a dsp.FIRRateConverter object using the toMultirate function. Specify the interpolation factor as 7, decimation factor as 3, and scale the passband gain by the interpolation factor.

firrcScaledGain = toMultirate(designedFilter,...
    InterpolationFactor=7,DecimationFactor=3,...
    ScaleByInterpolationFactor=true)

firrcScaledGain = 
  dsp.FIRRateConverter with properties:

   Main
    InterpolationFactor: 7
       DecimationFactor: 3
        NumeratorSource: 'Property'
              Numerator: [-6.9520e-04 -0.0111 -0.0219 0.0105 0.0914 0.0953 -0.1165 -0.3830 -0.2000 0.7448 1.9973 2.5854 1.9973 0.7448 -0.2000 -0.3830 -0.1165 0.0953 0.0914 0.0105 -0.0219 -0.0111 -6.9520e-04]

  Show all properties

Create another instance of the dsp.FIRRateConverter object with the same design specifications, but do not scale the passband gain of the filter.

firrcunityGain = toMultirate(designedFilter,...
    InterpolationFactor=7,DecimationFactor=3,...
    ScaleByInterpolationFactor=false)

firrcunityGain = 
  dsp.FIRRateConverter with properties:

   Main
    InterpolationFactor: 7
       DecimationFactor: 3
        NumeratorSource: 'Property'
              Numerator: [-9.9314e-05 -0.0016 -0.0031 0.0015 0.0131 0.0136 -0.0166 -0.0547 -0.0286 0.1064 0.2853 0.3693 0.2853 0.1064 -0.0286 -0.0547 -0.0166 0.0136 0.0131 0.0015 -0.0031 -0.0016 -9.9314e-05]

  Show all properties

Visualize the frequency response of these filters using filterAnalyzer. Note the difference in the passband gain for both these filters.

filterAnalyzer(firrcScaledGain,firrcunityGain)

Input Arguments

digiFiltObj — Digital FIR filter

digitalFilter object

Digital FIR filter, specified as a digitalFilter object. Use the designfilt function in the form digiFiltObj = designfilt(firResp,Name=Value) to create the digital filter object with the FIR response type. Customize the filter using the name-value arguments.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: multiFiltObj = toMultirate(digiFiltObj,InterpolationFactor=3,DecimationFactor=2,ScaleByInterpolationFactor=true)

InterpolationFactor — Interpolation factor

1 (default) | positive integer

Interpolation factor of the multirate filter object, specified as a positive integer. The values of the InterpolationFactor and DecimationFactor arguments must not have any common factors, that is, gcd(InterpolationFactor,DecimationFactor) must equal 1.

Data Types: single | double

DecimationFactor — Decimation factor

1 (default) | positive integer

Decimation factor of the multirate filter object, specified as a positive integer. The values of the InterpolationFactor and DecimationFactor arguments must not have any common factors, that is, gcd(InterpolationFactor,DecimationFactor) must equal 1.

Data Types: single | double

ScaleByInterpolationFactor — Option to scale passband gain

true (default) | false

Option to scale the passband gain by the interpolation factor, specified as one of these:

• true –– The multirate filter object scales its passband gain by the interpolation factor that you specify in the InterpolationFactor argument.

• false –– The multirate filter object maintains its passband gain at unity.

Data Types: logical

Output Arguments

multiFiltObj — Multirate filter object

dsp.FIRRateConverter | dsp.FIRInterpolator | dsp.FIRDecimator | dsp.FIRFilter

Multirate filter object, returned as one of these filter System objects:

• dsp.FIRRateConverter –– InterpolationFactor > 1, DecimationFactor > 1

• dsp.FIRInterpolator –– InterpolationFactor > 1, DecimationFactor = 1

• dsp.FIRDecimator –– InterpolationFactor = 1, DecimationFactor > 1

• dsp.FIRFilter –– InterpolationFactor = 1, DecimationFactor = 1

Version History

Introduced in R2025a