How do I get frequency response as values from multibandParametricEQ System object?

https://jp.mathworks.com/help/audio/ref/multibandparametriceq-system-object.html

I cant visualize the response using visualize(mPEQ). But I want "values" as [h,w]. How do I get?

Answer 1

[Kei Otsuka]

To extract frequency response, modifying or adding your own function to multibandParametricEQ.m might be helpful.

For example, you can use computefreqz, one of the dsp.util.FilterVisualizer object function to calculate frequency response within a multibandParametricEQ.

?

#1. Add following to visualize function defined in multibandParametricEQ.m

 fVector = logspace(log10(20),log10(Fs/2),NFFT);
 H = obj.visualObj.computefreqz(coeffs, fVector', Fs);
 data = 20*log10(abs(H));

#2. Add output arguments to visualize function

function [data, fVector] = visualize(obj,NFFT)

#3. Confirm if modified method works

mPEQ = multibandParametricEQ(...
  'NumEQBands',1,...
  'Frequencies',9.5e3,...
  'PeakGains',10);
[h, w] = visualize(mPEQ)
figure, semilogx(w,h)
ax = gca;
ax.YLim = [-25 25];
ax.XLim = [20 44100/2];
xlabel('Frequency (Hz)')
ylabel('Magnitude (dB)')
grid on
grid minor

[Hiroshi Iwamura]

Thank you for your reply.

I tried to add these lines at the end of "function [data, fVector] = visualize(obj,NFFT)".

fVector = logspace(log10(20),log10(Fs/2),NFFT ); H = obj.visualObj.computefreqz(coeffs, fVector', Fs ); data = 20*log10(abs(H));

And then I got error like "not found computefreqz".

Something wrong? (I'm using R2016a. But other error occurred in R2018a. )

But I found I can get filter coefficients as below.

[B,A] = coeffs(mPEQ);

So now I can draw arbitrary graph such as ...

Fs = 48000; f = logspace(1,5,4096); f(f>Fs/2) = [];

h_all = 0; for i=1:size(B,2) sosPEQ = [B(:,i),[1;A(:,i)]]; h = freqz(B(:,i),[1;A(:,i)],f,Fs); h_all = h_all + 20*log10(abs(h)); end figure semilogx(f,h_all)

That's fine to me!

Thanks a lot.

[Kei Otsuka]

That's great, thanks for sharing your experience with us.

&#01

The error you run into was because dsp.util.FilterVisualizer is not available on R2016a. This is just FYI, but you can use freqz instead like this;

fVector = logspace(log10(20),log10(Fs/2),NFFT);
H = freqz(coeffs{1}, [1;coeffs{2}], fVector', Fs);
data = 20*log10(abs(H));