cascade

Cascade digital filters

Since R2026a

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    Syntax

    dOut = cascade(d1,d2,...,dn)
    dOut = cascade(___,SampleRate=Fs)

    Description

    dOut = cascade(d1,d2,...,dn) cascades n digital filters into a digital filter cascade, dOut. You can cascade between 2 and 15 digitalFilter objects.

    example

    dOut = cascade(___,SampleRate=Fs) specifies the sample rate for the cascaded filter.

    example

    Examples

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    Open Live Script

    Design a lowpass IIR filter with passband and stopband frequencies of 0.65π rad/sample and 0.80π rad/sample, respectively. The passband ripple is 1 dB and the stopband attenuation is 50 dB. Plot the filter response.

    d1 = designfilt("lowpassiir", ...
    PassbandFrequency=0.65,StopbandFrequency=0.80, ...
    PassbandRipple=1,StopbandAttenuation=50);
freqz(d1)

    Figure contains 2 axes objects. Axes object 1 with title Phase, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Phase (degrees) contains an object of type line. Axes object 2 with title Magnitude, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Magnitude (dB) contains an object of type line.

    Design a bandstop IIR filter with passband ripples of 1 dB and stopband attenuation of 50 dB. The passband frequencies are 0.25π rad/sample and 0.34π rad/sample. The stopband frequencies are 0.36π rad/sample and 0.45π rad/sample. Plot the filter response.

    d2 = designfilt("bandstopiir", ...
    PassbandFrequency1=0.25,StopbandFrequency1=0.34, ...
    StopbandFrequency2=0.36,PassbandFrequency2=0.45, ...
    PassbandRipple1=1,StopbandAttenuation=50, ...
    PassbandRipple2=1);
freqz(d2)

    Figure contains 2 axes objects. Axes object 1 with title Phase, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Phase (degrees) contains an object of type line. Axes object 2 with title Magnitude, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Magnitude (dB) contains an object of type line.

    Cascade the lowpass IIR and bandstop IIR filters to form a cascaded filter. Plot the filter response.

    d3Norm = cascade(d1,d2)
    d3Norm = 
 digitalFilter cascade with properties:

   Stages:
                 Stage1: [1×1 digitalFilter]
                 Stage2: [1×1 digitalFilter]

   Specifications:
    NormalizedFrequency: 1

 Use filterAnalyzer to visualize filter
 Use filter to filter data


    freqz(d3Norm)

    Figure contains 2 axes objects. Axes object 1 with title Phase, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Phase (degrees) contains an object of type line. Axes object 2 with title Magnitude, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Magnitude (dB) contains an object of type line.

    Set the sample rate to 20 Hz and cascade the lowpass IIR and bandstop IIR filters to form a cascaded filter.

    Fs = 20;
d3Freq = cascade(d1,d2,SampleRate=Fs)
    d3Freq = 
 digitalFilter cascade with properties:

   Stages:
                 Stage1: [1×1 digitalFilter]
                 Stage2: [1×1 digitalFilter]

   Specifications:
    NormalizedFrequency: 0
             SampleRate: 20

 Use filterAnalyzer to visualize filter
 Use filter to filter data

    Input Arguments

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    Digital filter, specified as a digitalFilter object. Use designfilt to generate a digital filter based on frequency-response specifications.

    Example: d = designfilt("lowpassiir",FilterOrder=3,HalfPowerFrequency=0.5) specifies a third-order Butterworth filter with normalized 3 dB frequency 0.5π rad/sample.

    Sample rate of the cascaded filter, specified as one of these:

    • "auto" — cascade automatically sets the sample rate of the cascaded filter.

      • If all the digital filter inputs use normalized frequency, then cascade sets all the stages of dOut to use normalized frequency.

      • If some of the digital filter inputs have a common sample rate of Fs Hz and the rest of them use normalized frequency, then cascade uses Fs to set the sample rate of dOut.

      • If at least two of the digital filter inputs have a different sample rate, cascade errors out.

    • "normalized" — cascade sets all the stages of dOut to use normalized frequency.

    • Positive scalar — cascade uses the value specified in this argument to set the sample rate of dOut, in Hz.

    Data Types: char | string | single | double

    Output Arguments

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    Digital filter cascade, returned as a digitalFilter object.

    More About

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    Version History

    Introduced in R2026a

    See Also

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