Re: [Linphone-users] Noise and artefacts in sound

[J G Miller]

At 21:20h, on Friday, February 26, 2016,
in message <address@hidden>,
on the subject of "[Linphone-users] Noise and artefacts in sound",
Matthias Peter Walther explained -

 > I think it might be a problem between linphone and pulseaudio as Skype has
 > had similiar problems some years ago.

I think it may be a similar problem which I was suffering some time ago,
which despite trying all the different codecs in linphone and bitrate settings
resulted in audio distortion.

At the time I just could not understand why the audio was bad even when the best
quality or least quality codec was selected.

But, if the problem is correctly identified, it can be very easily fixed.

Pulseaudio can use different resampling methods and this is set in the file

               /etc/pulse/daemon.conf

If the resample method is set to use a method which puts too much demand on
your PC, then the audio is distorted.  The best compromise setting for my
system after various tests was found to be

              resample-method = speex-float-1

You may well be able to use a better quality method but not the absolute (?) 
best

                   src-sinc-best-quality

For further information see the table entry for "resample-method" with the
"Tip" highlighted in green at

      <https://wiki.archlinux.ORG/index.php/PulseAudio/Configuration>

and also the section "Re-sampling using up a lot of CPU time" at

      <https://wiki.gentoo.org/wiki/PulseAudio>

Note that lowering the resample-method specifiction from the absolute best will 
result
in a lowering of sound quality but if too high a resample-method is specified 
then the
sound quality will suffer from artefacts and so be distorted, so it all depends 
on
what your resources your PC can provide.

In fact to achieve the best sound quality means using the same sample-rate and 
sample-format
directly supported by the hardware and avoiding any resampling conversion at 
all.

The difficulty is getting pulseaudio not to resample from input to output has 
been
the most important criticism of pulseaudio by the sound quality experts and 
purists.

Hope this addresses your problem, which could be something else entirely ...