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Visualize frequency response of coupled allpass filter


fvtool(caf) displays the magnitude response of the coupled allpass filter System object™.

fvtool(caf,options) displays the response that is specified by the options. For example, to visualize the impulse response of a coupled allpass filter System object, set options to 'impulse'.

caf = dsp.CoupledAllpassFilter;


fvtool(____,Name,Value) visualizes the response of the filter with each specified property set to the specified value.

For more input options, see FVTool.


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Design a Butterworth lowpass filter of order 3. Use a coupled allpass structure with inner minimum multiplier structure.

Fs = 48000;    % in Hz
Fc = 12000;    % in Hz
frameLength = 1024;
[b,a] = butter(3,2*Fc/Fs);
AExp = [freqz(b,a,frameLength/2); NaN];
[c1,c2] = tf2ca(b,a);
caf = dsp.CoupledAllpassFilter(c1(2:end),c2(2:end));

Using the 'SubbandView' option of the dsp.CoupledAllpassFilter, you can visualize the lowpass filter output, the power complementary highpass filter output, or both using the fvtool.

To view the lowpass filter output, set 'SubbandView' to 1.


To view the highpass filter output, set 'SubbandView' to 2.


To view both the outputs, set 'SubbandView' to 'all', [1 2] or [1;2].


Input Arguments

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Input filter, specified as a dsp.CoupledAllpassFilter System object.

Example: caf = dsp.CoupledAllpassFilter; fvtool(caf)

Filter analysis options, specified as one of the following:

  • 'magnitude' –– Magnitude response

  • 'phase' –– Phase response

  • 'freq' –– Frequency response

  • 'grpdelay' –– Group delay

  • 'phasedelay' –– Phase delay

  • 'impulse' –– Impulse response

  • 'step' –– Step response

  • 'polezero' –– Pole zero plot

  • 'coefficients' –– Coefficients vector

  • 'info' –– Filter information

  • 'magestimate' –– Magnitude response estimate

  • 'noisepower' –– Round-off noise power spectrum

Example: fvtool(caf,'freq')

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.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: caf = dsp.CoupledAllpassFilter; fvtool(caf,'SubbandView','all','Arithmetic','single')

Specify the subband to be viewed. You can set this property to one of the following:

  • 1 –– Display the lowpass filter output.

  • 2 –– Display the power complimentary highpass filter output.

  • 'all', [1 2], [1;2] –– Display both the outputs.

Sampling rate, specified as a scalar. This value determines the Nyquist interval [–Fs/2 Fs/2] in which FVTool shows the frequency response of the filters in the channelizer.

Data Types: single | double

Specify the arithmetic used during analysis. The analysis tool assumes a double-precision filter when the arithmetic input is not specified and the filter System object is unlocked.

Version History

Introduced in R2013b

See Also