[Asterisk-Users] Echo after upgrade * 1.05 -> 1.06

[Florian Overkamp]

Hi, 

> -----Original Message-----
> > It could be deceiving indeed but the echo is slower than 
> > usually. I did downgrade to asterisk 1.0.5 and the echo is 
> less but still 
> > there. I did not downgrade zaptel as I think it's not 
> related. Or could it 
> > be a zaptel timing problem?

As someone mentioned the heart of the echocanceller is in the zaptel driver.
However, since your description looks like you're not using any Zap channel
in the path, it's not really likely to help.

> Increases and decreases in the time taken for the audio to 
> traverse the entire audio path will manifest themselves as 
> changes in percevability of echo. For example, changing from 
> an entirely uLaw path to a Speex-compressed path will 
> introduce additional non-trivial processing delays (see 'show 
> translation' in console). It's possible to have an echo on a 
> path that is initially perceived as sidetone suddenly become 
> a problem echo because of the introduction of additional 
> delays (ie. longer than the 20ms perceivability threshold).
> 
> Perhaps there compiler options have changed or the code has 
> become less efficient somewhere resulting in a greater delay. 
> If you haven't changed your configuration anywhere then try 
> comparing the output of 'show translation' on both versions 
> to verify the codecs are performing similarly.

I think with any VoIP setup, especially over the Internet, roundtrip delay
is very likely to be exceeding 20-25ms. Therefore it will never be perceived
as sidetone. Asterisk uses 20ms packet sizes, zo that's the minimum delay
we're looking at, not even accounting for transmission delays. Remember, the
20-25ms threshold is measured end to end, so you also need to account for
some milliseconds added by the VoIP-to-PSTN gateway and PSTN latency.

Florian