MATLAB: Manual Implementation of STFT of an audio signal.

audioout of memoryspectrogramstft

Hi ,
I have an Audio File whose spectrogram I want to find manually by calculating its STFT without using the inbuilt Spectrogram function. My steps can be mentioned as follows :-
a) I take samples out of the file in chunks of 1000 samples each and process them one by one. b) For each chunk , I find its STFT . c) I plot the magnitute squared of the STFT and hold that plot. d) I repeat the whole process again and again till all the samples of the audio file have been used.
However I face the following big problem :-
The process is never complete as everytime the computer runs out of memory. I try to use as few variables as possible and i clear the variables as soon as they are used. I also use the pack command before executing the program. However each time the computer almost hangs after some iterations. I think this is because the hold on command causes MATLAB to keep storing its previous plot data.
Is there any way around this issue ? Please enlighten. I am using an audio file of length 3.5 seconds at a sampling frequency of 44100 Hz.

Best Answer

Here's what you have to do, something like this:
    dt = 1/44100;
    t=0:dt:(117204*dt)-dt;                    
    x = chirp(t,1500,1,8000);
    S = zeros(501,117);
    windowlength = 1e3;
    k = 1;
    for jj = 1:117
        y = x(k:k+windowlength-1)';
        ydft = fft(y).*gausswin(1e3);
        S(:,jj) = ydft(1:501);
        k = k+windowlength;
    end
    F = 0:44100/1000:44100/2;
    T = 0:(1e3*dt):(117000*dt)-(1e3*dt);
    surf(T,F,20*log10(abs(S)),'EdgeColor','none')
    axis xy; axis tight; colormap(jet); view(0,90);
    xlabel('Time');
    ylabel('Frequency (Hz)');
Like I said, the segments do not overlap and I haven't been too careful with somethings, like whether I skip a sample between adjacent segments, but this is the general idea.
Related Question