[asterisk-dev] Jitterbuffer and FAXes with E1

Martin Vít vit at lam.cz
Wed Aug 1 14:40:49 CDT 2007

Klaus Darilion wrote:
> Zoa wrote:
>> Because the jitter buffer will never be size zero if its a fixed jitter 
>> buffer and will fluctuate if its a variable length jitter buffer.
>> So whatever you choose, the timing will be altered.
> I would think that a fixed jitter buffer is a fixed jitter buffer - 
> thus, only buffering voice frames adding a fixed delay (thus reducing 
> jitter but increasing delay) and do not change the audio data at all.
> A dynamic jitter buffer of course is bad. Because of the dynamic 
> behavior the audio samples have to be played back sometimes 
> faster/sometimes slower.

Finally as i wrote yesterday, the problem with faxes was in noise filter 
in sangoma HW echocan (fixed now).
> Thus, why does static jitter buffer manipulate the audio?
Static nor adaptive buffer does not manipulate frames. I've compare it 
frame by frame when the frame come to buffer and when it goes out.
> @Martin: What happens if you call the Milliwatt() application via a 
> jitter-buffer link? Do you hear frequency change?
Asterisk jitterbuffer is not capable of frequency change. It only 
buffers frames and if needed it sends info to translater to do PLC (if 
it is capable).

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