MATLAB: How to see freq response of a wave file

freq respnose

Hi i am having a wave file

I want to see its frequency response.

How can i see that

Best Answer

Again, if it's a signal and not a system, we don't say frequency response, but you can just use fft(). That gives you the DFT of the signal, so it is complex-valued. You can visualize the magnitude and phase responses separately. If your signal is real-valued, then the DFT is conjugate symmetric so you only have to keep the "positive" frequencies.

[y,fs] = wavread('foo.wav');
ydft = fft(y);
% I'll assume y has even length
ydft = ydft(1:length(y)/2+1);
% create a frequency vector
freq = 0:fs/length(y):fs/2;
% plot magnitude
subplot(211);
plot(freq,abs(ydft));
% plot phase
subplot(212);
plot(freq,unwrap(angle(ydft))); 
xlabel('Hz');

Related Solutions

MATLAB: Extracting the fundamental frequency of a .wav file

Here is an example you can modify with your input y

For even length y:

    Fs = 1000;
    t = 0:0.001:1-0.001;
    y = cos(2*pi*100*t)+randn(size(t));
    ydft = fft(y);
    freq = 0:Fs/length(y):Fs/2;
    ydft = ydft(1:length(y)/2+1);
    plot(freq,abs(ydft))
    [maxval,idx] = max(abs(ydft));
    freq(idx)  %this is frequency corresponding to max value

For odd length y

    t = 0:0.001:1;
    y = cos(2*pi*100*t)+randn(size(t));
    ydft = fft(y);
    freq = 0:Fs/length(y):Fs/2;
    ydft = ydft(1:floor(length(y)/2)+1);
    [maxval,idx] = max(abs(ydft));
    freq(idx)  %this is frequency corresponding to max value

MATLAB: How to find max freq and lamdha min for a pulse

   ydft = fft(y);
   ydft = ydft(1:floor(length(ydft)/2)+1);
   [maxval,I] = max(abs(ydft));
   freq = 0:fs/length(y):fs/2;
   fprintf('Maximum at %2.3f Hz\n.', freq(I));

You would have been better with:

   t=0:ts:n/f-ts;
   y=15*(1-cos(2*pi*f*t/n)).*cos(2*pi*f*t);
   ydft = fft(y);
   ydft = ydft(1:length(ydft)/2+1);
   [maxval,I] = max(abs(ydft));
   freq = 0:fs/length(y):fs/2;
   fprintf('Maximum at %2.3f Hz\n.', freq(I));

Due to the spacing of the frequencies in the DFT. As far as the wavelength, you have not told us the propagation speed, which you have to in order to determine wavelength. If we assume that it is the speed of light, then

lambda = 3e8/freq(I);
fprintf('Wavelength is %3.2f meters.\n',lambda)

Best Answer

Related Solutions

MATLAB: Extracting the fundamental frequency of a .wav file

MATLAB: How to find max freq and lamdha min for a pulse

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