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katkost@3
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1 function y = stpt(x, w, N, H, t)
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katkost@3
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2 % Analysis/synthesis of a sound using the peaks
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katkost@3
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3 % of the short-time fourier transform
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katkost@3
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4 % x: input sound,
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5 % w: analysis window (odd size),
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6 % N: FFT size,
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7 % H: hop size,
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8 % t: threshold in negative dB,
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katkost@3
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9 % y: output sound
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katkost@3
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10 M = length(w); % analysis window size
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11 N2 = N/2+1; % size of positive spectrum
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katkost@3
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12 soundlength = length(x); % length of input sound array
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katkost@3
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13 hM = (M-1)/2; % half analysis window size
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katkost@3
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14 pin = 1+hM; % initialize sound pointer at the middle of analysis window
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katkost@3
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15 pend = soundlength-hM; % last sample to start a frame
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16 fftbuffer = zeros(N,1); % initialize buffer for FFT
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katkost@3
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17 yw = zeros(M,1); % initialize output sound frame
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katkost@3
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18 y = zeros(soundlength,1); % initialize output array
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katkost@3
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19 w = w/sum(w); % normalize analysis window
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20 sw = hanning(M); % synthesis window
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katkost@3
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21 sw = sw./sum(sw);
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katkost@3
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22 while pin<pend
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23 %-----analysis-----%
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24 xw = x(pin-hM:pin+hM).*w(1:M); % window the input sound
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25 fftbuffer(:) = 0; % reset buffer
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26 fftbuffer(1:(M+1)/2) = xw((M+1)/2:M); % zero-phase fftbuffer
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27 fftbuffer(N-(M-1)/2+1:N) = xw(1:(M-1)/2);
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28 X = fft(fftbuffer); % compute the FFT
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29 mX = 20*log10(abs(X(1:N2))); % magnitude spectrum of positive frequencies
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30 pX = unwrap(angle(X(1:N2))); % unwrapped phase spectrum
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katkost@3
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31 ploc = 1 + find((mX(2:N2-1)>t) .* (mX(2:N2-1)>mX(3:N2)) ...
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katkost@3
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32 .* (mX(2:N2-1)>mX(1:N2-2))); % peakss
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33 pmag = mX(ploc); % magnitude of peaks
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34 pphase = pX(ploc); % phase of peaks
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katkost@3
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35 %-----synthesis-----%
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36 Y = zeros(N,1); % initialize output spectrum
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37 Y(ploc) = 10.^(pmag/20).*exp(i.*pphase); % generate positive freq.
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38 Y(N+2-ploc) = 10.^(pmag/20).*exp(-i.*pphase); % generate negative freq.
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39 fftbuffer = real(ifft(Y)); % real part of the inverse FFT
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katkost@3
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40 yw((M+1)/2:M) = fftbuffer(1:(M+1)/2); % undo zero phase window
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katkost@3
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41 yw(1:(M-1)/2) = fftbuffer(N-(M-1)/2+1:N);
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katkost@3
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42 y(pin-hM:pin+hM) = y(pin-hM:pin+hM) + H*N*sw.*yw(1:M); % overlap-add
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katkost@3
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43 pin = pin+H; % advance sound pointer
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katkost@3
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44 end |
