Hi Arno,

On 14/04/2023 18:29, Arno ll wrote:
> Hi Maemo-Leste Community,
>
> Calls are working both ways on n900 with an acceptable sound quality.
>
> [snip]
>
> *Why it was not working in both ways ?*
>
> Audio recording through cmt_speech is not working with sample rates >
> 4000 Hz
> (8000 Hz is possible but needs some work)
>
> Forcing pulseaudio to allow 4000 Hz frequency with no resampling solves
> the main issue.

This is a great find and great news, and it's good to know that with
some hacks we can now get voice calls to work on the Nokia N900.

Pavel, I suggested to Arno that we can lower the latency in pulseaudio
and I think he said he got it down to 30ms (from 600ms) or so. It's not
a clear implementation yet (kind of hack), but he said the audio quality
was good. So we might be getting somewhere here.
I tried to force the latency to be low with this commit:
https://github.com/maemo-leste/libcmtspeechdata/commit/ba3d714a953bd083ea0b61b282daaf81e954cb4a
- but Arno reported it doesn't work well and makes things really choppy.
I read this article
https://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/Developer/Clients/LatencyControl/
and wrote the commit based on that. Maybe it's outdated info.


Looking at the other points in the email (that I snipped out), some
things we can do now:

* Correct permissions for /dev/cmtspeech through udev rules
* Figure out a clean way to have PA allow recording at 4000Hz
* Allow pulseaudio to talk to (read from) ofono
* Work on getting UCM2 for Nokia N900

It looks like even after that there will be some hacks required to get
this working, but maybe the above is a good start.

Regards,
Merlijn