| % Attempts to diagnose AEC problems from recorded samples |
| % |
| % out = echo_diagnostic(rec_file, play_file, out_file, tail_length) |
| % |
| % Computes the full matrix inversion to cancel echo from the |
| % recording 'rec_file' using the far end signal 'play_file' using |
| % a filter length of 'tail_length'. The output is saved to 'out_file'. |
| function out = echo_diagnostic(rec_file, play_file, out_file, tail_length) |
| |
| F=fopen(rec_file,'rb'); |
| rec=fread(F,Inf,'short'); |
| fclose (F); |
| F=fopen(play_file,'rb'); |
| play=fread(F,Inf,'short'); |
| fclose (F); |
| |
| rec = [rec; zeros(1024,1)]; |
| play = [play; zeros(1024,1)]; |
| |
| N = length(rec); |
| corr = real(ifft(fft(rec).*conj(fft(play)))); |
| acorr = real(ifft(fft(play).*conj(fft(play)))); |
| |
| [a,b] = max(corr); |
| |
| if b > N/2 |
| b = b-N; |
| end |
| printf ("Far end to near end delay is %d samples\n", b); |
| if (b > .3*tail_length) |
| printf ('This is too much delay, try delaying the far-end signal a bit\n'); |
| else if (b < 0) |
| printf ('You have a negative delay, the echo canceller has no chance to cancel anything!\n'); |
| else |
| printf ('Delay looks OK.\n'); |
| end |
| end |
| end |
| N2 = round(N/2); |
| corr1 = real(ifft(fft(rec(1:N2)).*conj(fft(play(1:N2))))); |
| corr2 = real(ifft(fft(rec(N2+1:end)).*conj(fft(play(N2+1:end))))); |
| |
| [a,b1] = max(corr1); |
| if b1 > N2/2 |
| b1 = b1-N2; |
| end |
| [a,b2] = max(corr2); |
| if b2 > N2/2 |
| b2 = b2-N2; |
| end |
| drift = (b1-b2)/N2; |
| printf ('Drift estimate is %f%% (%d samples)\n', 100*drift, b1-b2); |
| if abs(b1-b2) < 10 |
| printf ('A drift of a few (+-10) samples is normal.\n'); |
| else |
| if abs(b1-b2) < 30 |
| printf ('There may be (not sure) excessive clock drift. Is the capture and playback done on the same soundcard?\n'); |
| else |
| printf ('Your clock is drifting! No way the AEC will be able to do anything with that. Most likely, you''re doing capture and playback from two different cards.\n'); |
| end |
| end |
| end |
| acorr(1) = .001+1.00001*acorr(1); |
| AtA = toeplitz(acorr(1:tail_length)); |
| bb = corr(1:tail_length); |
| h = AtA\bb; |
| |
| out = (rec - filter(h, 1, play)); |
| |
| F=fopen(out_file,'w'); |
| fwrite(F,out,'short'); |
| fclose (F); |