[Speex-dev] SPEEX on iPhone ?

[Alexander Chemeris]

On Thu, Nov 13, 2008 at 11:23 AM, Vincent Burel
<vincent.burel at vb-audio.com> wrote:
>> 2008/11/13 Vincent Burel <vincent.burel at vb-audio.com>:
>> > could you explain why 44.1kHz is *not* recommended with SPEEX ?
>>
>> my understanding is that the speex modes are tuned for particular
>> sample rates, so using the 32kHz mode with 44.1kHz data will not yield
>> as good quality as using the 32kHz mode with 32kHz data.
>
> ok, it's strange, by nature, such compression algorithm are able to make
> down or upsampling very well...
> Do there is an impact on CPU load ?

Nothing strange if you ever worked with speech compression before.
Speech compression algorithms always are tunned to particular freq,
else they would take tons of time. That's because they use knowledge
that speech pitch (and other params) lies in well specified regions.
Thus if you feed algorithm with wrong freq, you'll fool it and it might
even not detect speech at all.

In short - you must do up/down-sampling by yourself. There're a lot of
nice libraries for this. One of them is libspeexdsp. ;)


-- 
Regards,
Alexander Chemeris.

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