Optimization team update (11/23 ~ 11/29)

Al Johnson openmoko at mazikeen.demon.co.uk
Sun Dec 7 18:26:51 CET 2008

On Sunday 07 December 2008, Neil Jerram wrote:
> 2008/12/2 Andy Green <andy at openmoko.com>:
> > "buzz / echo / hiss"... no software change can fix buzz.  It's baked
> > into the hardware and you will have to do fairly extreme meddling with
> > your soldering iron to impact it.
> Thanks, I hadn't seen that so clearly stated before!  (i.e. that buzz
> is known to be 100% a hardware issue).
> > "Echo" reacts to some tweaking in alsa and maybe Calypso firmware option
> > selection, I guess this turn up in rootfs images as best it can.
> OK, but do you need to be so imprecise about this?  What can't there
> be a definitive solution?

It depends partly on what you mean by a definitive solution. If you mean "one 
alsa state file that everyone's happy with" it'll never happen because 
the 'correct' volume level is subjective and depends on ambient noise among 
other variables outside our control. If you mean something that's reasonable 
out of the box and only needs a small tweak of the volume then my experience 
is we have had it since the calypso echo suppression was enabled.

It doesn't help that the echo suppression and noise reduction functions we 
need from the Calypso are undocumented. It seems there are some gain controls 
in the Calypso too. Some of us find that the echo suppression remains 
effective until a reboot while others report it only working for the first 
call, and we don't know the cause. There are several settings available for 
both echo suppression and noise reduction, and they have different audible 
characteristics. Generally the stronger the suppression the more audible its 
action. People don't agree on which ones sound acceptable, and which one you 
use can have a significant effect on the gain you can use before you start 
getting echo.

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