calypso hardware echo suppression?

Joerg Reisenweber joerg at
Wed Aug 27 19:37:43 CEST 2008

Am Mi  27. August 2008 schrieb Bruce Bertrand:
> On Wed, 2008-08-27 at 05:39 +0800, Joerg Reisenweber wrote:
> > Am Di  26. August 2008 schrieb Al Johnson:
> > > According to the 
> > audio 
> > > table has parameters for echo suppression and AGC. Does this mean that 
> > > GSM chipset has echo suppression hardware?
> > 
> > I guess that's actually the case.
> > I'm investigating (on low priority though) how to exploit these functions 
> > calypso chipset.
> > Any additional info / participation on task appreciated :-)
> > 
> > cheers
> > jOERG
> Just to be clear, echo suppression is not the same as echo
> cancellation.  
> In the latter, the output of the speaker is inverted and adaptively
> added to the mic input so as to cancel out acoustic coupling.
> Echo suppression simply tries to detect when you are silent (ie.
> listening to the other party), and mutes the mic input.  When you speak
> it unmutes the input.

Yup, thanks for this clarifying comment. 
We don't expect to see echo-cancellation in calypso - it's a very complicated 
and thus processing-power consuming task, that probably would need a 
dedicated DSP.
Echo-suppression OTOH is relatively simple and could be done "in software" 
even, by using Wolfson mixer's A/D-converter plus the input noisegate/ALC PGA 
As long as we don't suspend CPU during call that is.
I prefer to use any function built-in to calypso for this reason, as long as 
we get same performance as with A/D plus CPU.

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