23 lines
831 B
Matlab
23 lines
831 B
Matlab
% plot_specgram.m
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% David Rowe May 2017
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%
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% As the name suggests.....
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function S = plot_specgram(x, Fs=8000, fmin, fmax)
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step = fix(20*Fs/1000); # one spectral slice every 5 ms
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window = fix(160*Fs/1000); # 40 ms data window
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fftn = 2^nextpow2(window); # next highest power of 2
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[S, f, t] = specgram(x, fftn, Fs, window, window-step);
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S = abs(S(2:fftn/2,:)); # magnitude in range 0<f<=Fs/2 Hz.
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S = S/max(S(:)); # normalize magnitude so that max is 0 dB.
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S = max(S, 10^(-20/10)); # clip below -20 dB.
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S = min(S, 10^(-3/10)); # clip above -3 dB.
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imagesc (t, f, log(S)); # display in log scale
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set (gca, "ydir", "normal"); # put the 'y' direction in the correct direction
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if nargin > 2
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axis([0 max(t) fmin fmax])
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end
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xlabel('Time (s)'); ylabel('Freq (Hz)');
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endfunction
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