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1% Attempts to diagnose AEC problems from recorded samples
2%
3% out = echo_diagnostic(rec_file, play_file, out_file, tail_length)
4%
5% Computes the full matrix inversion to cancel echo from the
6% recording 'rec_file' using the far end signal 'play_file' using
7% a filter length of 'tail_length'. The output is saved to 'out_file'.
8function out = echo_diagnostic(rec_file, play_file, out_file, tail_length)
9
10F=fopen(rec_file,'rb');
11rec=fread(F,Inf,'short');
12fclose (F);
13F=fopen(play_file,'rb');
14play=fread(F,Inf,'short');
15fclose (F);
16
17rec = [rec; zeros(1024,1)];
18play = [play; zeros(1024,1)];
19
20N = length(rec);
21corr = real(ifft(fft(rec).*conj(fft(play))));
22acorr = real(ifft(fft(play).*conj(fft(play))));
23
24[a,b] = max(corr);
25
26if b > N/2
27      b = b-N;
28end
29printf ("Far end to near end delay is %d samples\n", b);
30if (b > .3*tail_length)
31      printf ('This is too much delay, try delaying the far-end signal a bit\n');
32else if (b < 0)
33      printf ('You have a negative delay, the echo canceller has no chance to cancel anything!\n');
34   else
35      printf ('Delay looks OK.\n');
36      end
37   end
38end
39N2 = round(N/2);
40corr1 = real(ifft(fft(rec(1:N2)).*conj(fft(play(1:N2)))));
41corr2 = real(ifft(fft(rec(N2+1:end)).*conj(fft(play(N2+1:end)))));
42
43[a,b1] = max(corr1);
44if b1 > N2/2
45      b1 = b1-N2;
46end
47[a,b2] = max(corr2);
48if b2 > N2/2
49      b2 = b2-N2;
50end
51drift = (b1-b2)/N2;
52printf ('Drift estimate is %f%% (%d samples)\n', 100*drift, b1-b2);
53if abs(b1-b2) < 10
54   printf ('A drift of a few (+-10) samples is normal.\n');
55else
56   if abs(b1-b2) < 30
57      printf ('There may be (not sure) excessive clock drift. Is the capture and playback done on the same soundcard?\n');
58   else
59      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');
60      end
61   end
62end
63acorr(1) = .001+1.00001*acorr(1);
64AtA = toeplitz(acorr(1:tail_length));
65bb = corr(1:tail_length);
66h = AtA\bb;
67
68out = (rec - filter(h, 1, play));
69
70F=fopen(out_file,'w');
71fwrite(F,out,'short');
72fclose (F);
73