[Asterisk-Users] G729 Codec

[Steve Underwood]

Andres wrote:

> steve at daviesfam.org wrote:
>
>> On Tue, 3 Aug 2004, Steve Underwood wrote:
>>
>>  
>>
>>> Eh? G.729 has no particular features to allow more effective packet 
>>> loss concealment. iLBC has, but at the cost of a substantially 
>>> higher bit rate. In fact G.711 is a little ahead of G.729 in the 
>>> regard, since packets are completely independant. The smoothing in 
>>> G.729 means you need the previous packet to decode the current one 
>>> properly.
>>>   
>>
>>
>> For IAX2, at least, Asterisk oes not use the lost-packet-concealment 
>> of any codec.  This is because the incoming frames "clock" Asterisk.  
>> For iLBC's lost packet concealment to work, Asterisk would have to 
>> start calling the decoder with a NULL at the point when the missing 
>> packet shold have arrived.
>>  
>>
> This certainly explains why we get terrible audio at 10% packet loss 
> between Asterisk servers between 2 end points using iLBC, but if we 
> use 2 SPA2000s using G.729 to commincate directly with each other (and 
> having the same 10% packet loss), they sound pretty good.  We had been 
> trying to figure why iLBCs loss concealment wasn't helping much.  I 
> was never able to explain this until now:)
>
> Thanks.
>
If you have 10% packet loss G.729 should sound awful. Are you really 
getting 10% packet loss in the G.729 case? If not, why does iLBC give 
that? Is the higher bit rate of iLBC pushing things over your available 
bandwidth limit? Seems pretty odd.

Regards,
Steve