[speex-dev] reommended settings for low bitrate voicecom codec ?

[Peter Kirk]

Am Dienstag, 13. Mai 2003 04:00 schrieb Jean-Marc Valin:
> > What I did to find this out:
> > I comprared a speex AVB with 6.3 KBit/sec (total, overhead for packets
> > and stuff included) and the 6.3 Kbit/sec Celp Codec vom hawkvoice (
> >  http://www.hawksoft.com/hawkvoice) and the result is quite favorable for
> > hawkvoice.
> > I cant believe that this is *normal* speex behavior, please correct me if
> > that hawkvoice thing just performs better on that bandwidth.
>
> First, what do you mean by AVB (average bit-rate?)? Also, when you say
> 6.3 kbps with overhead how much of that is the Speex bandwidth (helps me
> get an idea of the expected quality).

Ok, now you are asking internal stuff, Im only a tester that wants to do some 
*research* to take load off the developer(s). But I asked about this stuff 
and I know this:
yes, perceptual enhancement is ON.
yes, constant bitrate is being used
no, dtx is not used, as teamspeak has its own discontinuity detection and 
doesnt send voice streams at all then.

About the *real* (without overhead) bitrate speex is set to I can only guess 
for the 6.3 speex...I know for a fact that the 4.5 kbps speex codec teamspeak 
also has in the testclient is realy the lowest speex setting (2.15 kbps) - 
Doing some maths and asuming same overhead on both bandwidth settings 4.0 
kbps for the speex 6.3 codec used in teamspeak...Id love to hear some tips on 
how to improve its quality :o). If anybody experienced in this needs to try 
it out Im confident I could get you a test-client for this purpose.

> > Could you please tell me what options are best for what codec bandwidth ?
> > Im figuring something is wrong since speex sounds worse than hawkvoice on
> > the low bandwidth...I would appreciate if youd post the *recommended*
> > settings for 5, 10, 15 and 20 KBit narrowband AVB speex (used in a
> > voicecom that shouldnt take too many cpu cylces of the game).
>
> First, in the decoder make sure that you turn perceptual enhancement
> *on* (it is off by default when using the libspeex API). To do that:
> int tmp=1;
> speex_decoder_ctl(decoder_state, SPEEX_SET_ENH, &tmp);
>
> For the rest, all you need to do is decide whether you want constant
> bit-rate or variable bit-rate and whether you want discontinuous
> transmission (DTX). You might also want to play with the "complexity"
> value, but the default is usually OK.
>
> 	Jean-Marc


-- 
The meek don't want it.

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