Plotting matrix as spectrogram

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Sania Gul 2022-8-26

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https://ww2.mathworks.cn/matlabcentral/answers/1786805-plotting-matrix-as-spectrogram

评论： Robert U 2022-8-26

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.

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Robert U 2022-8-26

在 MATLAB Online 中打开

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 2022-8-26

[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

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采纳的回答

Robert U 2022-8-26

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https://ww2.mathworks.cn/matlabcentral/answers/1786805-plotting-matrix-as-spectrogram#answer_1034275

在 MATLAB Online 中打开

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