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 To :  "Yate mailing list" <yate@v...>
 From :  "Andrew McDonald" <andrew.mcdonald@n...>
 Subject :  [yate] Bug in conference smart mixing
 Date :  Mon, 28 Aug 2006 11:32:36 +0800

While testing the 1.0 version of the conference module I set up a call to a conference room that had smart=yes, with no other attendees. This meant the return audio should be golden silence. After about 13 seconds of call time, bursts of noise (inbound audio) could be heard. 

This was caused by a slight bug in the current implementation. 

Basically ConfRoom::mix() checks hasSignal() before mixing in audio from a channel, however ConfConsumer::dataForward() does not make such a check before subtracting out the individual channel's audio. This means in cases where hasSignal() is false, the inbound channel noise is effectively added (inverted) into the outbound audio mix. 

The inward audio was typically (non-golden) silence or comfort noise.

The timeline is explained by the fact that it takes the m_noise2 value about 13 seconds to converge to the average energy m_energy2 of the noise of the inbound call and thereafter it varies slightly above and below the average energy value. Thus for a call with comfort noise at the level set in our inbound all,  hasSignal() returns true for the first 13 seconds and then returns true or false in a semi-random pattern thereafter. 

As a quick fix I added an equivalent hasSignal() check to the audio subtraction of ConfConsumer::dataForward().

<         if (i < n)
<             val -= d[i];
>         if (hasSignal() && (i < n))
>         {
>             val -= d[i];
>         }



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