Background amplification and voice blur on phone call

[Paul Fertser]

jeremy jozwik <jerjoz.forums at gmail.com> writes:
> ok, ive got my gsmhandset.state mono value at 2 now. place call
> freerunner [a] to nokia [b]

I hope you know about the "pretty" diagram with alsa control names [1]
(yes, it's for gta02). I suggest you look at it once more and tweak
appropriate settings with alsamixer during the call.

> [b] signal is super loud, which is odd because i would think it would
> be very quiet.

That's the difference you see between extra-cap units and
not. Supposedly you have a capless unit and is using too much
amplification for the earpiece in the codec. (FYI nobody knows for
sure and there's no way to know which units have those stupid caps and
which do not. Looks like all A7 units have them, as probably most of A5;
my A6 doesn't)

> and it sounds as if the freerunner is recording in a
> pvc pipe.

Please pay attention that you have 2 (almost) independent problems to
solve:
1. Hearing the other side
2. Providing the other side a good signal from the mic

I suggest you do it one by one.

> and the  Echo Suppression and Noise Reduction from
> http://wiki.openmoko.org/wiki/Hardware:AT_Commands

These commands have an immediate effect, you can use them in
mickeyterm while a call is ongoing to change the behaviour. In my
experience what they do is cut the signal altogether if the level is
too low (that is, to not amplificate ambient noise/street
sounds/whatever) and normalize sounds of normal level. So basically
you need to tweak the recording level so that noise is still
considered noise and cut and your voice is considered a useful signal
and normalized. And yes, %0187 makes voice sound a little bit harsh,
that's a price for the echo suppression. Also the louder your
earpiece, the more echo suppression is needed. If you feel creative,
you can try to make some rubber isolation between the case parts
because echo occures because of the acoustic feedback via the
case. Removing the screwes also reduces echo.

CLVL affects only loudness of the signal output from calypso to the
codec input.

[1] http://wiki.openmoko.org/wiki/Neo_1973_audio_subsystem

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