diff extra codes/stft_primer_ejemplo.m @ 3:1c0f36c348d4

extra code for matlab

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/extra codes/stft_primer_ejemplo.m	Sat Apr 20 13:03:01 2013 +0100
@@ -0,0 +1,34 @@
+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
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