echo (was: ASU software - pre-pre-release impressions)

[Mike Montour]

Crane, Matthew wrote:
> I've noticed that with GSM calls in general there is sometimes an echo.  It can be very pronouced or barely noticable.  It may be hw or sw, but it may not have anything to do with either caller's phone.
> 
> If it doesn't happen consistently and is not reproducable, it's likely the network.  IMHO.

In some cases it might be from the network, if it was using a buggy or
mis-calibrated echo-cancellation algorithm. However the Neo itself is
also quite capable of generating an echo - some of the sound coming out
of its speaker is picked up by its microphone, and is then encoded and
sent back to the other caller. In my tests the echo went away when I
muted the Neo's speaker or microphone, so it did not seem to be a
network issue.

The audio coupling between the Neo's speaker and microphone can be
measured independently of the GSM stuff, e.g. with the 'Jaaa' audio
analyzer from http://www.kokkinizita.net/linuxaudio/ or with 'xoscope'.
Various ALSA mixer controls will affect the level of the coupled signal,
but these also affect the intended sound paths (loudness of the speaker
and sensitivity of the microphone). The mixer settings have to be
selected to give the best compromise between these factors. I hope that
the overall audio quality will be "good enough" once the mixer settings
have been optimized, but I am not yet confident of this.

Audio-quality reports from other Freerunner owners would be appreciated.