[speex-dev] Videoconferencing with speex and jabber
Jean-Marc.Valin at USherbrooke.ca
Tue Nov 18 17:50:04 PST 2003
> 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.
Wow, these are pretty high bit-rates. Though I have never tested your 32
kbps ADPCM codec, my guess is that Speex 24.6 kbps probably has a higher
quality than an ADPCM codec at 32 kbps.
> 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.
If you're concerned with low-end microphones, I think you should try the
denoiser that's currently in the 1.1.x branch (try 1.1 because later
versions include minor changes in the API).
> 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!
I'm mostly trying to be informative here. I'm well aware that Speex is
not the best codec out there.
> 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.
Can you tell me what the problem was? It shouldn't be harder to get
wideband to work than narrowband.
> We may try another crack at getting it to operate with wideband in Speex
> since you say it is so much more clean/better.
Definitely. Wideband and narrowband is day and night. At 27.8 kbps (and
possibly lower), you can get much better quality than anything you can
do with narrowband (see the samples on the website).
Jean-Marc Valin, M.Sc.A., ing. jr.
Université de Sherbrooke, Québec, Canada
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