view extra/gong.m @ 13:844d341cf643 tip

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function y = stpt(x, w, N, H, t)
% Analysis/synthesis of a sound using the peaks
% of the short-time fourier transform
% x: input sound, w: analysis window (odd size), N: FFT size, H: hop size,
% t: threshold in negative dB, 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 at the 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
sw = hanning(M); % synthesis window
sw = sw./sum(sw);
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 fftbuffer
fftbuffer(N-(M-1)/2+1:N) = xw(1:(M-1)/2);
X = fft(fftbuffer); % compute the FFT
mX = 20*log10(abs(X(1:N2))); % magnitude spectrum of positive frequencies
pX = unwrap(angle(X(1:N2))); % unwrapped phase spectrum
ploc = 1 + find((mX(2:N2-1)>t) .* (mX(2:N2-1)>mX(3:N2)) ...
.* (mX(2:N2-1)>mX(1:N2-2))); % peaks
pmag = mX(ploc); % magnitude of peaks
pphase = pX(ploc); % phase of peaks
%-----synthesis-----%
Y = zeros(N,1); % initialize output spectrum
Y(ploc) = 10.^(pmag/20).*exp(i.*pphase); % generate positive freq.
Y(N+2-ploc) = 10.^(pmag/20).*exp(-i.*pphase); % generate negative freq.
fftbuffer = real(ifft(Y)); % real part of the inverse FFT
yw((M+1)/2:M) = fftbuffer(1:(M+1)/2); % undo zero phase window
yw(1:(M-1)/2) = fftbuffer(N-(M-1)/2+1:N);
y(pin-hM:pin+hM) = y(pin-hM:pin+hM) + H*N*sw.*yw(1:M); % overlap-add
pin = pin+H; % advance sound pointer
end