1 files changed, 72 insertions, 0 deletions
diff --git a/code/libspeex/echo_diagnostic.m b/code/libspeex/echo_diagnostic.m
new file mode 100644
index 0000000..aebf390
--- /dev/null
+++ b/code/libspeex/echo_diagnostic.m
@@ -0,0 +1,72 @@
+% 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);