Plotting matrix as spectrogram

13 views (last 30 days)
Sania Gul
Sania Gul on 26 Aug 2022
Commented: Robert U on 26 Aug 2022
I want to plot a matrix of 256* 16, as spectrogram. But when I use surf command to do so, I got spectrogram of size 343*436. I want the image to be of same size as that of matrix i.e. 256*16. Kindly suggest any solution without cropping or resizing the image as both of them distorts the quality.
  3 Comments
Robert U
Robert U on 26 Aug 2022
testData = randn(256,16);
fh = figure;
ah = axes(fh);
surf(ah,testData);
I was not able to reproduce the described error by the given information.
Kind regards,
Robert
Sania Gul
Sania Gul on 26 Aug 2022
[Q,F,T] = spectrogram(audio,hann(512),256,512,Fs,'yaxis');
Q=Q(1:256,:);
F=F(1:256);
figure(2)
D=surf(T,F,log(abs(Q).^2));
colormap parula
shading interp
view([0 90])
axis tight
set(gca,'xtick',[])
set(gca,'ytick',[])
export_fig AA.jpg -native -c[31 52 46 72]% top right bottom left
% reading the image
I=imread('AA.jpg');
>>The value of I=343x436x3 uint8, but the size of matrix Q was only 256x16, and I want 'I' to be also 256x16x3 uint8

Sign in to comment.

Accepted Answer

Robert U
Robert U on 26 Aug 2022
Hi Sania Gul,
The values you provide are not consistent. I assume your "audio" is a vector of a certain length N, sampled with the frequency Fs.
Applying the function spectrogram with the window-length 512, overlap 256 and NFFT of 512 lead certainly to the dimension of Q of NFFT/2+1 = 257 and ((N - 512)/(512-256)).
If you want Q to be 257 x 16 you would have to provide a snippet of roughly 4600 samples.
fs = 60e3;
t = 0:1/fs:4599/fs;
x1 = vco(sawtooth(2*pi*t,0.5),[0.1 0.4]*fs,fs);
[Q,F,T] = spectrogram(x1,hann(512),256,512,fs,'yaxis');
size(Q)
ans = 1×2
257 16
Kind regards,
Robert
  4 Comments
Sania Gul
Sania Gul on 26 Aug 2022
Tnk u soooo much, but how to get rid of the frame around the spectrogram without using the export.fig?
Robert U
Robert U on 26 Aug 2022
There is still some manual work required to get the desired result.

Sign in to comment.

More Answers (0)

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!