[speex-dev] Videoconferencing with speex and jabber

[Allen Drennan]

Hello Jean-Marc,

Regarding your question - a little background on the various choices,
Fair Quality is 15kbps Speex narrowband, Good Quality is 24kbps Speex
narrowband, High Quality is 32kbps ADPCM from HawkVoice and Toll Quality
is 64kbps PCM.

We also have 10 other codecs within the product including GSM, LPC and
others that we currently do not expose.

To us, quality is a combination of perceived voice quality and latency.
Celp based codecs sound great when the tolerance range for the recording
input is within the range of human voice.  However, they tend to degrade
when people use low end microphones that introduce lots of ambient
noise.  We have found that at least half of people use low-end or table
microphones and quality of course suffers.  ADPCM and PCM are much
better in this regard because of the way they operate.  They are also
better with latency (of course) because there is less coding/decoding
going on.

This isn't a knock against Speex, as it works great at the bitrate and
we are very happy with it's performance vs. other voice coders like GSM
and are grateful for your efforts!

We authored the current Delphi header translation and DLL stuff for
Speex that is being used by lots of people.  While our header supports
Speex wideband, we have never been able to get wideband to work.

We may try another crack at getting it to operate with wideband in Speex
since you say it is so much more clean/better.

>Just curious, any reason you're not using Speex for high quality (at
18.2 and 24.6 kbps, I can't distinguish the coded from the original and
15 kbps is pretty close)? I'm also not sure I see the idea of narrowband
PCM either, since you can get better quality at lower bit-rates by
encoding in wideband (16 kHz).

        Jean-Marc


-- 
Jean-Marc Valin, M.Sc.A., ing. jr.
LABORIUS (http://www.gel.usherb.ca/laborius)
Université de Sherbrooke, Québec, Canada

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