[Speex-dev] AEC strangest behavior

[Jean-Marc Valin]

On 2010-03-16 14:22, Josh Gargus wrote:
>> If more than one speaker receives the *same* signal, it doesn't
>> matter the number of speakers. It only gets tricky when the
>> speakers are playing slightly different signals (e.g. from a stereo
>> song).
>
> Does "tricky" mean that the Speex AEC won't handle such situations
> well?  Or just that you had to be extraordinarily clever in order to
> make Speex AEC handle such situations well?  :-)

Tricky here means that I got it to work in some scenarios, but it likely 
will not work out-of-the-box and you'd be on your own because I don't 
have time to help on that.

> We're thinking of using Speex AEC in the context of a virtual
> environment using OpenAL for spatialized sound.  Is there any hope
> that this could work?  What could we do (short of not spatializing
> sound input) to make things easier for the AEC algorithm?

As long as the spatialization transfer function is constant, then a mono 
AEC will work. If you only have a few different transfer functions, that 
may be an option. For time-varying spatialization with many (>2) 
channels, forget about AEC unless you're willing to spend a *lot* of 
time on that.

	Jean-Marc

> Thanks, Josh
>
>
>
>> Jean-Marc
>>
>> Quoting Greger Burman<greger at mobile-robotics.com>:
>>
>>> One thing I can think of is if you are using two or more
>>> speakers. If the speakers are not at the exact same distance from
>>> the mic, you will get more than one echo. AEC can not handle
>>> that. Try disconnecting all but one speaker and see if it makes
>>> any difference.
>>>
>>> cheers Greger
>>>
>>> 2010/3/15 Anton A. Shpakovsky<saa at tomsksoft.com>
>>>
>>>> Hello.
>>>>
>>>> I have the following situation. AEC is used in network chat
>>>> software
>>>>
>>>> over DirectSound API. Echo and reference signals are almost
>>>> aligned
>>>>
>>>> (delay is no more than 30ms). When echo is emulated in
>>>> notebook
>>>>
>>>> (built-in speakers + mic) everything goes fine and echo is
>>>> cancelled.
>>>>
>>>> But when configuration includes stand-alone speakers and mic no
>>>> echo is
>>>>
>>>> removed. Audio is in 22050 hz at 16 bit mono format, number of
>>>> samples
>>>>
>>>> to process were 441 and tail was used 4096.
>>>>
>>>>
>>>>
>>>> Dumps are here:
>>>> http://rapidshare.com/files/317389207/speex_AEC_test.rar.html
>>>>
>>>> nb_*** - working configuration (notebook)
>>>>
>>>> sa_*** - standalone speakers with no echo removed
>>>>
>>>>
>>>>
>>>> Can it be because of differences in fixed and arbitrary
>>>> acoustic systems?
>>>>
>>>> I will appreciate any of your advises or thoughts.
>>>>
>>>>
>>>>
>>>> Thanks!
>>>>
>>>>
>>>>
>>>> Anton A. Shpakovsky
>>>>
>>>> Multimedia Software Developer
>>>>
>>>>
>>>>
>>>> _______________________________________________ Speex-dev
>>>> mailing list Speex-dev at xiph.org
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>>>>
>>>
>>
>>
>>
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