[Speex-dev] Sampling Rate

[Alain M.]

What would be speex configuration recomended for Telefone/Voip quality
voice? With a quality just a little better/similar then G.729? or GSM?

is there a comparison chart somewhere, but telephone quality oriented?

Thanks,
Alain

Tom Grandgent escreveu:
> 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
> 
> <khaynes at kirkgames.com> wrote:
>> Hi,
>>
>> I'm attempting to use speex for voice chat in my game.
>>
>> I'm capturing audio from the mic using OpenAL 1.1 in 16 bit mono. What 
>> sample rate is recommended for capturing from the mic? Which would be 
>> better: 11025 samples per second, or 22050 samples per second of 16 bit 
>> mono audio with respect to then encoding/decoding it with speex? I'm 
>> using 11025 to reduce bandwidth at the moment to capture.
>>
>> Given your answer to the above question, what is the most efficient 
>> frame size for encoding the samples to speex frames? The sample code 
>> uses 160 samples (320 bytes) of 16 bit audio samples, which are then 
>> encoded to 200 bytes of encoded data. Is a 30% reduction in data pretty 
>> standard? How do I use speex most efficiently?
>>
>> Kirk
>>
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