58 lines
2.1 KiB
Matlab
58 lines
2.1 KiB
Matlab
function y = chanvocoder(carrier, modul, chan, numband, overlap)
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% y = chanvocoder(carrier, modul, chan, numband, overlap)
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% The Channel Vocoder modulates the carrier signal with the modulation signal
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% chan = number of channels (e.g., 512)
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% numband = number of bands (<chan) (e.g., 32)
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% overlap = window overlap (e.g., 1/4)
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if numband>chan
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error('# bands must be < # channels')
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end
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[rc, cc] = size(carrier);
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if cc>rc
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carrier = carrier';
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end
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[rm, cm] = size(modul);
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if cm>rm
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modul = modul';
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end
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st = min(rc,cc); % stereo or mono?
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if st~= min(rm,cm)
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error('carrier and modulator must have same number of tracks');
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end
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len = min(length(carrier),length(modul)); % find shortest length
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carrier = carrier(1:len,1:st); % shorten carrier if needed
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modul = modul(1:len,1:st); % shorten modulator if needed
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L = 2*chan; % window length/FFT length
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w = hanning(L);
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if st==2
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w=[w w];
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end % window/ stereo window
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bands = 1:round(chan/numband):chan; % indices for frequency bands
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bands(end) = chan;
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y = zeros(len,st); % output vector
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ii = 0;
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while ii*L*overlap+L <= len
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ind = round([1+ii*L*overlap:ii*L*overlap+L]);
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FFTmod = fft( modul(ind,:) .* w ); % window & take FFT of modulator
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FFTcar = fft( carrier(ind,:) .* w ); % window & take FFT of carrier
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syn = zeros(chan,st); % place for synthesized output
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for jj = 1:numband-1 % for each frequency band
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b = [bands(jj):bands(jj+1)-1]; % current band
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syn(b,:) = FFTcar(b,:)*diag(mean(abs(FFTmod(b,:))));
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end % take product of spectra
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midval = FFTmod(1+L/2,:).*FFTcar(1+L/2,:); % midpoint is special
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synfull = [syn; midval; flipud( conj( syn(2:end,:) ) );]; % + and - frequencies
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timsig = real( ifft(synfull) ); % invert back to time
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y(ind,:) = y(ind,:) + timsig; % add back into time waveform
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ii = ii+1;
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end
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y = 0.8*y/max(max(abs(y))); % normalize output
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