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