[pulseaudio-discuss] Problems with Speex Resamplers

[Colin Guthrie]

Hi Everyone,

Just wanted to let people know that we've uncovered some problems with
the speex resamplers in PulseAudio

The problem generally manifests itself when having the following setup.

* Server Sample Rate: 44100
* Resampler: speex-* (both fixed and float)
* Playing a 48000 stream

The problem only really manifests itself in the first 500ms or so of the
stream and then generally clears itself out so it's not always obvious
when listening to e.g. music, but for event sounds etc. it's quite
apparent (KDE event sounds are technically played via
Phonon->GStreamer->PA, and as GST lets PA do the resampling, it will
exhibit the problem - FWIW, I believe this pipeline for event sounds is
insane and I am actively trying to change that[1], but it's beside the
point).


I opened this bug https://bugzilla.gnome.org/show_bug.cgi?id=636294 to
report a GST problem but it very much is a problem in either Speex or
our use of it. The above contains some test cases to recreate the issue
easily via gst but it would be possible to cause this via other systems too.


I have tried:
 1. Calling speex_resampler_skip_zeros() on init and reset: no change.
 2. Applying a fix found here.
http://thread.gmane.org/gmane.comp.audio.compression.speex.devel/6833
(no replies on the speex-dev list to that one... not sure if it's needed
etc.


Nothing above seemed to help.

Any advice or debugging tips welcome. The trivial and sinc resamplers
seem to work fine FWIW.


Cheers

Col


References
1. http://thread.gmane.org/gmane.comp.kde.users.multimedia/5979


-- 

Colin Guthrie
gmane(at)colin.guthr.ie
http://colin.guthr.ie/

Day Job:
  Tribalogic Limited [http://www.tribalogic.net/]
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  PulseAudio Hacker [http://www.pulseaudio.org/]
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