[Speex-dev] AEC stops working in 1.2-rc1?

[Benny Prijono]

On Mon, Aug 11, 2008 at 12:34 PM, Jean-Marc Valin <
jean-marc.valin at usherbrooke.ca> wrote:

> OK, here's what happens. There is indeed a small difference between
> beta3 and rc1, but the fundamental problem isn't there. I've attached
> plots of the speaker signal (blue) alongside the mic signal (green). You
> can see the delay is in the order of 1000 samples. That's way too much
> to do anything useful because the tail doesn't even "see" the echo. You
> need to reduce that delay if you want the AEC to work. See the manual.
>
>
Sorry I don't get you. I can make sense of that *if* you're talking about
testecho sample application, since in testecho the tail is set to 1024
samples.

But, as I explained, I used my test program for producing the result, and
there I set the tail length to 200ms (1600 samples). *And*, in addition to
that, I delay the frames that's fed to speex_echo_cancellation() by 100ms,
to reflect the playback/recording delay when the mic.pcm file was recorded.
This means, if I play the frame now, I will give it to
speec_echo_cancellation() 100ms later (similar to your PLAYBACK_DELAY in
mdf.c). So this is equal to shifting the blue signal in your graph to the
right by 100ms.

It's easier to understand with testecho perhaps. I did the following changes
to testecho.c:

 - changed the frame size and tail length:
    #define NN 80
    #define TAIL 1600
 - apply the delay before entering the "while" loop by adding:
     {
         int i;
         for (i=0; i<10; ++i)
           fread(ref_buf, sizeof(short), NN, ref_fd);
     }

The result, testecho from beta3 can cancel the echo, while the rc1 version
can't.

I hope I made it clearer this time.

Thanks
 Benny
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