# Why do I receive an error when I use the SPECTROGRAM

Why do I receive an error when I use the SPECTROGRAM function if the length of the window is equal to the signal length in **Signal Processing Toolbox** 6.13 (R2010a)?

I try to plot the spectrogram of a signal using the following code (data file attached):

load emg;x = emg;lenx = length(x);window = ones(1, lenx);nfft = lenx/8; fs = 1000;noverlap = 32;F = [1:1:fs/2];spectrogram(x,window,noverlap,F,fs)

The error I receive is the following:

??? Error using ==> surf at 78

Z must be a matrix, not a scalar or vector.

Error in ==> spectrogram>displayspectrogram at 250

hndl = surf(args{:},’EdgeColor’,’none’);

Error in ==> spectrogram at 184 displayspectrogram(t,f,Pxx,isFsnormalized,faxisloc);

# ANSWER

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The ability to have the length of the signal to be the same as the length of the window is not available for the SPECTROGRAM function in **Signal Processing Toolbox** 6.13 (R2010a).

As a workaround, use the IMAGESC function as follows:

T = 0:0.001:2;X = chirp(T,100,1,200,'q');[S, F, T, P] = spectrogram(X,128,120,128,1E3); imagesc(F, T(1), 10*log10(P(:,1).')); axis xy; axis tight; xlabel('Frequency (Hz)');ylabel('Time');title('Quadratic Chirp');