[asterisk-dev] Jitterbuffer and FAXes with E1

Klaus Darilion klaus.mailinglists at pernau.at
Thu Aug 2 01:38:16 CDT 2007

Hi Martin!

Thanks for the update.

Now, with the sangoma problems fixed, do you see any improvement for fax 
transmissions by using the jitter buffer?


Martin Vít schrieb:
> 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.
> Hi,
> 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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