[Ekiga-list] Aliasing in audio codecs

[Jean-Marc Valin]

If that's what I think it is, it's not related to Speex, iLBC or any
other audio codec. It's actually ALSA that finds that your soundcard
cannot do 8/16 kHz, so it automatically does resampling (usually to 48
kHz). The only problem is that ALSA uses LINEAR INTERPOLATION RESAMPLING
which is about the worst you can do. The only solutions are 1) to fix
ALSA 2) use PulseAudio 3) implement decent resampling code in Ekiga
(I've got an alpha resampler in Speex svn now).

	Jean-Marc

Damien Sandras a écrit :
> Le vendredi 26 janvier 2007 à 23:08 +0100, go music a écrit :
>> I'm discovering Ekiga using it with success including audio/video for
>> two days now on a Mandriva 2007 system, and I really congratulate
>> everyone who give and have given their contribution to that great
>> project! Diamondcard works fine as well BTW.
>> Here is my question for upcoming developments.
>> I have noticed that both SPEEX (8 and 16kHz bandwidth) and the iLBC
>> codecs produce aliasing either due to inadapted frequency filtering of
>> the audio bandwidth with respect to the raw sample rate or low (8?)
>> bit conversion without interpolation or both. Is there any way to fix
>> this? it would really be necessary to improve the audio quality of
>> these codecs, and can be achieved by using matched filters and
>> interpolation. 
> 
> That's probably a question for Jean-Marc Valin (I'm cc'ing him).