annotate extra/stft_primer_ejemplo.m @ 13:844d341cf643 tip

Back up before ISMIR

function y = stft(x, w, N, H)
% Analysis/synthesis of a sound using the short-time fourier transform
% x: input sound, w: analysis window (odd size), N: FFT size, H: hop size
% y: output sound
M = length(w); % analysis window size
N2 = N/2+1; % size of positive spectrum
soundlength = length(x); % length of input sound array
hM = (M-1)/2; % half analysis window size
pin = 1+hM; % initialize sound pointer in middle of analysis window
pend = soundlength-hM; % last sample to start a frame
fftbuffer = zeros(N,1); % initialize buffer for FFT
yw = zeros(M,1); % initialize output sound frame
y = zeros(soundlength,1); % initialize output array
w = w/sum(w); % normalize analysis window
while pin<pend
%-----analysis-----%
xw = x(pin-hM:pin+hM).*w(1:M); % window the input sound
fftbuffer(:) = 0; % reset buffer
fftbuffer(1:(M+1)/2) = xw((M+1)/2:M); % zero-phase window in fftbuffer
fftbuffer(N-(M-1)/2+1:N) = xw(1:(M-1)/2);
X = fft(fftbuffer); % compute FFT
mX = 20*log10(abs(X(1:N2))); % magnitude spectrum of positive frequencies
pX = unwrap(angle(X(1:N2))); % unwrapped phase spect. of positive freq.
%-----synthesis-----%
Y = zeros(N,1); % initialize output spectrum
Y(1:N2) = 10.^(mX/20).*exp(i.*pX); % generate positive freq.
Y(N2+1:N) = 10.^(mX(N2-1:-1:2)/20).*exp(-i.*pX(N2-1:-1:2));
% generate neg.freq.
fftbuffer = real(ifft(Y)); % inverse FFT
yw(1:(M-1)/2) = fftbuffer(N-(M-1)/2+1:N); % undo zero-phase window
yw((M+1)/2:M) = fftbuffer(1:(M+1)/2);
y(pin-hM:pin+hM) = y(pin-hM:pin+hM) + H*yw(1:M); % overlap-add
pin = pin+H; % advance sound pointer
end