Get STFT plot with matrix Input

Hello,

I am working with a radar output Q/ I matrix and I want to apply stft on the complex matrix (I + j Q) using matlab.

The stft function didn't accept Matrix Input. Is there a way to do it ?

Thank you so much in advance :)

Answer 1

[nur dsc]

Hi Nour,

You do not need a matrix format actually. I+j*Q is also in vector format and you can apply stft this complex data.

If you have orijinal x signal you can use hilbert(x).

result = hilbert(x)

then you can apply stft to result.

Answer 2

[Priyanshu Mishra]

Hi Nour,

In the documentation page of stft, under the input argument section, it is mentioned that x can take vector and matrix both. You may refer to examples given in the documentation page of stft.

[Nour]

Thank you for you answer :) But when I apply stft function to that matrix I got this error. Do you have any idea how to fix this ?

[Priyanshu Mishra]

So the documentation I shared with you are for MATLAB2019b. It is released now. The stft and istft functions now accept multichannel signals as input. You can download MATLAB2019b.

[Nour]

Perfect I used this version and it works, but it does not plot the result. Do you have any idea how to get the plot? Thank you so much in advance :)

[Sara James]

The stft function in 2019b only supports plotting of vector inputs. If you want to use the convenience plot of stft for your matrix input, you could do so within a for loop. Alternatively, you could specify your own plots using pcolor and subplot like in the following example:

fs = 1e3; % Sampling frequency (Hz)
t = 0:1/fs:1-1/fs; % Time (sec)

x = [chirp(t,100,1,300,'quadratic',45,'concave');
      chirp(t,200,1,600,'quadratic',[],'convex');
      chirp(t,300,1,500,'logarithmic')]'; % Multi-channel signal
  
[S,F,T] = stft(x,fs,'Window',hamming(128,'periodic'),'OverlapLength',50);
smag = mag2db(abs(S)); % Convert to dB
caxisLims = max(smag(:)) + [-60 0]; % Color axis limits

figure('Name','STFT')
numChannels = size(x,2);
for ii = 1:numChannels
    subplot(2,2,ii)
    pcolor(T,F,smag(:,:,ii))
    xlabel('Time (s)')
    ylabel('Frequency (Hz)')
    shading flat
    colorbar
    caxis(caxisLims)
    title(sprintf('Channel %d',ii))
end