plotting spectrogram for 3d matrix

Hi

I want to make a spectrogram on a matrix and not on a vector

Is there such a possibility?

% this is work for Vector:

r = randi([-130,-50],1,100);
s = spectrogram(r);

spectrogram(r,'yaxis')

But ,i what plot this:

% this is NOT work for matrix:

r = randi([-130,-50],100,100);
s = spectrogram(r);

spectrogram(r,'yaxis')

Another question

Is the MATLAB function also correct for LOG [dBm]?

Because in the first example I in the fig positive values ,

tnx

[MarKf]

spectrogram returns the time-frequency spectrum of one signal timeseries, so would a matrix be considered a single signal (in which case spectrogram(r(:)) would work, but it's unlikely this is case), or is each row (or column) a signal from which you want to extract the spectrograms? In that case use a loop or something like fieldtrip. Or maybe you want a periodogram (no time dim).

Log works, the positive values in the result are to be expected by the conversion solution of a non-perfect signal.

[shahar]

@Marco Fuscà

I thought I would be able to produce a graph similar to spectrum instruments that produce a spectrogram

Answer 1

[Nicolas Douillet]

As Marco said, spectrogram takes a vector as input, not matrix. However depending on how your signals are stored in your data matrix you have, you have four different possibilities :

I.1 Case your signal had actually been reshaped in a matrix :

s = spectrogram(r(:))

I.2 Symetric matrix case; same as previous but you will transpose r matrix before :

r = r';
s = spectrogram(r(:))

II.1 Case your matrix actually contains several signals you want to compute the spectrogram and each signal corresponds to one row of the matrix; if you want the spectrogram of the ith row / signal then just write :

s = spectrogram(r(i,:)) % i is the matrix row index

(In a loop or in a cell array function)

II.2 Case each column of the matrix if a signal :

s = spectrogram(r(:,j)) % j is the matrix column index

(In a loop or in a cell array function)

Hope this help. Good work.