freqz

Compute frequency response

Syntax

[H,f] = freqz(obj)

[H,f] = freqz(obj,ind)

[H,f] = freqz(___,N=n)

freqz(___)

Description

[H,f] = freqz(obj) returns a matrix of complex frequency responses for each filter designed by obj.

[H,f] = freqz(obj,ind) returns the frequency response of filters with indices corresponding to the elements in vector ind.

[H,f] = freqz(___,N=n) returns the N-point complex frequency response.

freqz(___) with no output arguments plots the frequency response of the filter bank.

Examples

Frequency Response of gammatoneFilterBank

Create a gammatoneFilterBank object. Call freqz to get the complex frequency response, H, of the filter bank and a vector of frequencies, f, at which the response is calculated. Plot the magnitude frequency response of the filter bank.

gammaFiltBank = gammatoneFilterBank;
[H,f] = freqz(gammaFiltBank);

plot(f,abs(H))
xlabel("Frequency (Hz)")

To get the frequency response of a subset of filters in the filter bank, specify the second argument as a row vector of indices between one and the number of filters in the filter bank. Get the frequency response of the 10th filter in the filter bank and plot the magnitude frequency response.

[H,f] = freqz(gammaFiltBank,10);

plot(f,abs(H))
xlabel("Frequency (Hz)")

To specify the number of points in the frequency response, use the N name-value argument. Specify that the frequency response contains 128 points. Plot the magnitude frequency response.

[H,f] = freqz(gammaFiltBank,N=128);

plot(f,abs(H))
xlabel("Frequency (Hz)")

To visualize the magnitude frequency response only, call freqz without any output arguments. Plot the magnitude frequency response, in dB, of filters 20, 21, and 22 with 1024 points.

freqz(gammaFiltBank,[20,21,22],N=1024)

Frequency Response of octaveFilterBank

Create an octaveFilterBank object. Call freqz to get the complex frequency response, H, of the filter bank and a vector of frequencies, f, at which the response is calculated. Plot the magnitude frequency response in dB.

octFiltBank = octaveFilterBank;
[H,f] = freqz(octFiltBank);

plot(f,20*log10(abs(H)))
xlabel("Frequency (Hz)")
ylabel("Magnitude (dB)")
set(gca,XScale="log")
axis([10 octFiltBank.SampleRate/2 -100 2])

To get the frequency response of a subset of filters in the filter bank, specify the second argument as a row vector of indices between one and the number of filters in the filter bank. Get the frequency response of the 5th filter in the filter bank and plot the magnitude frequency response in dB.

[H,f] = freqz(octFiltBank,5);

plot(f,20*log10(abs(H)))
xlabel("Frequency (Hz)")
ylabel("Magnitude (dB)")
set(gca,XScale="log")
axis([10 octFiltBank.SampleRate/2 -100 2])

To specify the number of points in the frequency response, use the N name-value argument. Specify that the frequency response contains 8192 points. Plot the magnitude frequency response in dB.

[H,f] = freqz(octFiltBank,N=8192);

plot(f,20*log10(abs(H)))
xlabel("Frequency (Hz)")
ylabel("Magnitude (dB)")
set(gca,XScale="log")
axis([10 octFiltBank.SampleRate/2 -100 2])

To visualize the magnitude frequency response only, call freqz without any output arguments. Plot the magnitude frequency response, in dB, of filters 4, 5, and 6 with 1024 points.

freqz(octFiltBank,[4,5,6],N=1024)

Input Arguments

obj — Object to get filter frequency responses from

gammatoneFilterBank | octaveFilterBank

Object to get filter frequency responses from, specified as an object of gammatoneFilterBank or octaveFilterBank.

ind — Indices of filters to calculate frequency responses from

1:N (default) | row vector of integers with values in the range [1, N]

Indices of filters to calculate frequency responses from, specified as a row vector of integers with values in the range [1, N]. N is the total number of filters designed by obj.

n — Number of points in frequency response

8192 (default) | positive integer

Number of points in the frequency response, specified as a positive integer.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Output Arguments

H — Complex frequency response of each filter

matrix

Complex frequency response of each filter, returned as an M-by-N matrix. M is the number of points, specified by n. N is the number of filters, which is either length(ind) or, if ind is not specified, the total number of filters in the filter bank.

Data Types: double

f — Frequencies at which response is computed (Hz)

column vector

Frequencies at which the response is computed in Hz, returned as a column vector.

Data Types: double

Version History

Introduced in R2019a