getNumStages

Get number of stages in digital filter cascade

Since R2026a

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    Syntax

    n = getNumStages(d)

    Description

    n = getNumStages(d) returns the number of stages in a digital filter cascade d.

    example

    Examples

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    Open Live Script

    Get the number of stages and CTF sections of a lowpass filter, a bandstop filter, and a lowpass-bandstop cascaded filter.

    Design two digital filters with these specifications:

    • 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.

    • 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.

    d1 = designfilt("lowpassiir", ...
    PassbandFrequency=0.65,StopbandFrequency=0.80, ...
    PassbandRipple=1,StopbandAttenuation=50);
d2 = designfilt("bandstopiir", ...
    PassbandFrequency1=0.25,StopbandFrequency1=0.34, ...
    StopbandFrequency2=0.36,PassbandFrequency2=0.45, ...
    PassbandRipple1=1,StopbandAttenuation=50, ...
    PassbandRipple2=1);

    Cascade the lowpass IIR and bandstop IIR filters to form a single cascaded filter. Calculate the number of stages and CTF sections. The cascaded filter has two stages and 10 CTF sections.

    d3 = cascade(d1,d2)
    d3 = 
 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


    numStages3 = getNumStages(d3)
    numStages3 = 
2

    [B3,A3] = ctf(d3);
numCTFsections3 = size(B3,1)
    numCTFsections3 = 
10

    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.

    Output Arguments

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    Number of stages in filter, returned as a positive integer.

    Version History

    Introduced in R2026a

    See Also

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