[Asterisk-Users] G729 vs. gsm

[Andrew Kohlsmith]

On May 27, 2005 01:27 pm, Michael D Schelin wrote:
> I have used G729 and it sounds almost as good as G711U. The problem is
> the way Asterisk uses it. It does not sound robotic and it's not suppose
>   to sound that way. Most Carriers want the calls to be in g711u so
> thats why I use G711u otherwise I want to save money on bandwidth. G729
> on Asterisk adds latency. this could be one of your problems. Also you
> will not get music on hold to play well with G729.

Latency is increased any time you have to take time to mangle bits.  This 
means going from any codec to any other codec.  Of course, some codecs take 
more time to mangle the bits than others, and this is the case with any 
decent-sounding compressed codec such as gsm or g729 or even ilbc or speex.

If the latency's too high, get a more powerful system.  The codecs are all 
coded fairly well so there's not much to be gained by trying to reimplement 
the codec.

Also g729 sounds nothing like toll quality; the compressed codecs are able to 
compress so well by throwing away large chunks of the already limited trunk 
bandwidth.  As a result, music sounds like crap on most compressed codecs.  
Personally I find gsm plays on hold music quite well (obviously not amazingly 
well and nowhere near as good as ulaw), but yes g729 mangles it pretty 
well.  :-)

It's not an Asterisk problem, and it's not a g729 problem.  Hell, it's not 
even an implmentation issue.  It's the nature of the beast.

-A.