Short time fourier transformation inspired by Hristo Zhivomirov on Matlab Central
Copyright (c) 2015, Hristo Zhivomirov All rights reserved.
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clear, clc, close all
% load a .wav file
[x, fs] = wavread('track.wav'); % get the samples of the .wav file
x = x(:, 1); % get the first channel
xmax = max(abs(x)); % find the maximum abs value
x = x/xmax; % scalling the signal
% define analysis parameters
xlen = length(x); % length of the signal
wlen = 1024; % window length (recomended to be power of 2)
h = wlen/4; % hop size (recomended to be power of 2)
nfft = 4096; % number of fft points (recomended to be power of 2)
% define the coherent amplification of the window
K = sum(hamming(wlen, 'periodic'))/wlen;
% perform STFT
[s, f, t] = stft(x, wlen, h, nfft, fs);
% take the amplitude of fft(x) and scale it, so not to be a
% function of the length of the window and its coherent amplification
s = abs(s)/wlen/K;
% correction of the DC & Nyquist component
if rem(nfft, 2) % odd nfft excludes Nyquist point
st(2:end, :) = s(2:end, :).*2;
else % even nfft includes Nyquist point
s(2:end-1, :) = s(2:end-1, :).*2;
end
% convert amplitude spectrum to dB (min = -120 dB)
s = 20*log10(s + 1e-6);
% plot the spectrogram
figure(1)
imagesc(t, f, s)
set(gca,'YDir','normal')
set(gca, 'FontName', 'Times New Roman', 'FontSize', 14)
xlabel('Time, s')
ylabel('Frequency, Hz')
title('Amplitude spectrogram of the signal')
handl = colorbar;
set(handl, 'FontName', 'Times New Roman', 'FontSize', 14)
ylabel(handl, 'Magnitude, dB')