84 lines
2.9 KiB
Matlab
84 lines
2.9 KiB
Matlab
|
|
function [y, modul, carrier, output] = 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) (e.g., 32)
|
|
% overlap = window overlap (e.g., 1/4)
|
|
|
|
if numband>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 the 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
|
|
modul_out = zeros(len,st); % modulator signal for output
|
|
carrier_out= zeros(len,st); % carrier signal for output
|
|
|
|
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
|
|
modul_out(ind,:) = modul(ind,:); % save modulator signal for output
|
|
carrier_out(ind,:) = carrier(ind,:); % save carrier signal for output
|
|
ii = ii+1;
|
|
end
|
|
y = 0.8*y/max(max(abs(y))); % normalize output
|
|
|
|
% Plotting
|
|
t = (0:len-1) / st; % time vector
|
|
|
|
% Plot modulator, carrier, and output signals
|
|
subplot(3,1,1);
|
|
plot(t, modul_out);
|
|
title('Modulator Signal');
|
|
xlabel('Time (s)');
|
|
ylabel('Amplitude');
|
|
|
|
subplot(3,1,2);
|
|
plot(t, carrier_out);
|
|
title('Carrier Signal');
|
|
xlabel('Time (s)');
|
|
ylabel('Amplitude');
|
|
|
|
subplot(3,1,3);
|
|
plot(t, y);
|
|
title('Output Signal');
|
|
xlabel('Time (s)');
|
|
ylabel('Amplitude');
|