Volume controls

Dieter Spaar spaar at openmoko.org
Sun Nov 23 22:38:14 CET 2008

Michael 'Mickey' Lauer wrote:
> Oh they do. The change is audible. It's still no clear which of the settings 
> provide the best compromise though. I have studied said part of the code, but 
> I'm wondering whether you can toggle echo cancellation and noise reduction 
> completely independent or whether one category of these commands always turn 
> off the other category and whether N0187 is the only one that toggles both 
> ON, e.g. it's unclear whether you can set both to ON but with varying 
> reduction (-6,-12,-18). What do you think?
Good question. But not that easy to answer. As far as I am aware
the echo cancellation and noise reduction are done by the DSP inside
the Calypso. We don't have documentation for this part. Additionally
this DSP has its code in ROM and only patches are applied to it by
the GSM firmware (of course no sources for this part ;-).

So there is only the "trial-and-error" approach to find out what
the DSP can do regarding audio and if it can do more than what
is already available.

BTW, some audio analog part (e.g. amplification) is done by the
TLW3014 and besides the echo cancellation and noise reduction
there are also digital filters (FIR) in the audio path where the
coefficients can all be set.

Best regards,

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