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 http://wiki.openmoko.org/wiki/GTA01_gsm_modem#AT.40AUL the > > audio > > > table has parameters for echo suppression and AGC. Does this mean that the > > > 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 of > > 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 amp. 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. cheers jOERG
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