[Speex-dev] Comparison

[Joe T]

Dear Jean-Marc,

Thanks and appreciate the explanation.

I am asking this because it is believed that Skype is using some iLBC and
iSAC since GlobalIPSound listed Skype as a partner.


Thanks,
Joe

-----Original Message-----
From: Jean-Marc Valin [mailto:Jean-Marc.Valin at USherbrooke.ca] 
Sent: Friday, June 10, 2005 12:24 PM
To: joe_anny at yahoo.com.sg
Cc: speex-dev at xiph.org
Subject: Re: [Speex-dev] Comparison

Hi,

First, you can see a comparison of the codec features at
http://www.speex.org/comparison.html

As for quality/bitrate, the first thing is that Speex supports a lot
more settings (from 4 to 42 kbps) and does wideband (16 kHz sampling),
which iLBC doesn't do. I've only tested iLBC once, but I've found that
Speex has a better quality for the same bit-rate (or lower bit-rate for
the same quality). This is mainly due to the fact that iLBC is designed
to encode frames independently (more on this below). Even from their
site, you see that even at 13.3 or 15 kbps (they don't specify which),
they have the same quality as G.729A at 8 kbps. 

Now, their point is that since each frame is independent, the codec is
more robust to packet losses which is good for VoIP. However, in my
opinion (and that of others) is that the price in terms of bit-rate is
too high and you might as well just add redundancy by transmitting some
packets more than once (as proposed in
http://www.icassp2004.com/Papers/viewpapers.asp?papernum=3280 ). For
instance, if it goes to 20% packet loss, then transmitting 8 kbps Speex
packets twice (4% effective loss) will be much better than iLBC at 15
kbps.

Regarding CPU utilization, I have no idea what iLBC requires. For a PC I
don't think it actually matters and for embedded systems, then you have
to pay for a fixed-point iLBC license (Speex includes the fixed-point in
the same code).

	Jean-Marc

P.S. Of course you can say I'm biased since I'm the author of Speex, but
since you posted to speex-dev, you probably expected that anyway.

Le vendredi 10 juin 2005 à 09:35 +0800, Joe T a écrit :
> Hi,
> 
> Is there any comparison made between Speex and iLBC free codec? 
> How would they compare in terms of quality, bitrate and CPU
> utilization?
> 
> Thanks, 
> Joe
> 
> _______________________________________________
> Speex-dev mailing list
> Speex-dev at xiph.org
> http://lists.xiph.org/mailman/listinfo/speex-dev
-- 
Jean-Marc Valin <Jean-Marc.Valin at USherbrooke.ca>
Université de Sherbrooke

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