[Asterisk-Users] Audio quality

[SteveK]

On May 13, 2005, at 8:36 PM, Scott Lamb wrote:

> I'm a new Asterisk user. I've managed to set it up to do everything  
> I want except sound good. Currently, Asterisk sounds considerably  
> worse than my cell phone. I know VOIP can be _better_ than my cell  
> phone, because I've heard Skype do it. (Using 32k iLBC, I believe.)
>


(1) Your cellphone, and the entire PSTN, use an 8khz sample rate.   
Going over public phone networks, you'll never get more than 8khz  
sampling.  Using asterisk and uLaw, assuming there's no problems on  
the network, should give you sound equivalent to a land-line phone,  
which also uses 8kHz uLaw (or, aLaw if you're outside USA, but the  
sound is basically going to be the same).

(2) I think skype uses, in it's "best" mode, wideband (16khz) iLBC.   
[you wrote "32k", where it isn't clear whether you were talking about  
kHz or kbps].


Asterisk doesn't presently have support for sample rates other than  
8kHz.   I don't expect that 1.2 will have this either, as you either  
need to (a) hack it in using a different "codec" type for each sample- 
rate, where there are only 16 audio codec type slots in the current  
API, or (b) make incompatible changes to many APIs, and probably to  
the IAX2 protocol as well.

The iaxclient library has some support for different sample rates in  
the audio layer, and it's codec drivers, but does not yet have any  
support for these at the protocol layer.

-SteveK