[Speex-dev] Sampling Rate

Steve Kann stevek at stevek.com
Mon Dec 11 15:34:11 PST 2006


You can always sample from the mic at a higher rate, and resample for  
use with speex.  If you sample at 32K or 48K, you can easily resample  
down to 16K, and use that for wideband speex..

On Dec 11, 2006, at 6:11 PM, <khaynes at kirkgames.com> wrote:

> It seems that I only have the following values available for  
> sampling from the mic.
> "The value must be 8000, 11025, 22050, 32000, 44100, or 48000"
> Which leaves 8000 and 32000 for use with speex. I think since this  
> is a game and not a voice application, I'm stuck using the 8kHz  
> rate. What speex setting would you recommend I use for the best  
> quality/performace, what frame size (number of samples) to send to  
> the encoder, etc..
>> Kirk,
>> Speex was designed for 8kHz, 16kHz, and 32kHz sample rates.  If you
>> don't use one of these sample rates, you'll be messing up important
>> assumptions deep within the codec.  Why these sample rates?  It's
>> telecommunications tradition, rather than PC audio tradition.
>> If you want an efficient and high quality format for voice chat, try
>> 16kHz with VBR quality 6.  You should see around a 10:1 compression
>> ratio when someone is talking.  That is, around 25kbps would be a
>> rough peak using these settings.
>> If that's too much bandwidth for you, you can cut it by almost half
>> using VBR quality 2.  (The loss of quality will be noticible to most
>> people using headsets.  It is less noticible when using speakers.)
>> For further bandwidth savings you could use 8kHz, but it's too much
>> of a quality hit to be worth it in my opinion.
>> Tom
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