[Speex-dev] SPEEX on iPhone ?

[Vincent Burel]

----- Original Message ----- 
From: "Alexander Chemeris" <Alexander.Chemeris at sipez.com>
To: "Vincent Burel" <vincent.burel at vb-audio.com>
Cc: "Conrad Parker" <conrad at metadecks.org>; <speex-dev at xiph.org>; "Jean-Marc
Valin" <jean-marc.valin at usherbrooke.ca>
Sent: Thursday, November 13, 2008 11:31 PM
Subject: Re: [Speex-dev] SPEEX on iPhone ?


> 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.

yes, also you could add : if i had any clue in audio domain ! :-)

> 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.

Do you mean that speex is working at 44.1 Khz like at 32Khz without
samplerate conversion ?

It seems you suggest that working with 44.1 Khz signal instead of 32Khz
(wich is the native samplingrate for the ultra -wide-band mode as far as i
understand) ask for more CPU load. Since YOU have already worked with SPEEX,
do you know how much CPU load it takes ? 10% more ? 50% more ?

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

So you confirm that SPEEX does not do it ? it works with 44.1Khz like
with 32KHz ?

thanks by advance
Regards
Vincent Burel