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freqz

CWT filter bank frequency responses

Syntax

[psidft,f] = freqz(fb)
freqz(fb)

Description

example

[psidft,f] = freqz(fb) returns the frequency responses for the wavelet filters, psidft, and the frequency vector, f, for the continuous wavelet transform (CWT) filter bank, fb. Frequencies are in cycles/sample or Hz. If you specify a sampling period, the frequencies are in cycles/unit time where the time unit is the unit of the duration SamplingPeriod.

The frequency responses, psidft, are one-sided frequency responses for the positive frequencies. For the analytic wavelets supported by cwtfilterbank, the frequency responses are real-valued and are equivalent to the magnitude frequency response.

freqz(fb) with no output arguments plots the magnitude frequency responses for the CWT filter bank, fb.

Examples

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Create a CWT filter bank. Set the voices per octave to 14, the sampling frequency to 1000 Hz, and frequency limits to range from 200 Hz to 300 Hz.

fb = cwtfilterbank('VoicesPerOctave',14,'SamplingFrequency',1000,'FrequencyLimits',[200 300])
fb = 
  cwtfilterbank with properties:

      VoicesPerOctave: 14
              Wavelet: 'morse'
    SamplingFrequency: 1000
       SamplingPeriod: []
         PeriodLimits: []
         SignalLength: 1024
      FrequencyLimits: [200 300]
        TimeBandwidth: 60
    WaveletParameters: []
             Boundary: 'reflection'

Obtain the frequency responses for the filter bank. Plot the frequency responses.

[psidft,f] = freqz(fb);
plot(f,psidft)
grid on
title('Frequency Responses')
xlabel('Frequency (Hz)')
ylabel('Magnitude')

Input Arguments

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Continuous wavelet transform (CWT) filter bank, specified as a cwtfilterbank object.

Output Arguments

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Frequency responses of a CWT filter bank, returned as a real-valued Ns-by-M matrix where Ns is the number of scales. If the filter bank Boundary is 'reflection', M is equal to 2*floor(SignalLength/2)+1. If the filter bank Boundary is 'periodic', M is equal to floor(SignalLength/2)+1.

The frequency responses, psidft, are one-sided frequency responses for the positive frequencies. For the analytic wavelets supported by cwtfilterbank, the frequency responses are real-valued and are equivalent to the magnitude frequency response.

Frequencies, in cycles/sample or Hz, returned as a real-valued vector. If the filter bank Boundary is 'reflection', f has length 2*floor(SignalLength/2)+1. If the filter bank Boundary is 'periodic', f has length floor(SignalLength/2)+1.

If you specify a sampling period, the frequencies are in cycles/unit time where the time unit is the unit of the duration SamplingPeriod.

Data Types: double

Introduced in R2018a