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