[Asterisk-Users] X100P Echo was: USB Headsets (Plantronics DSP-400)

[willy at yponeinc.com]

Hi,
The echo problem is the X100P.  The hybrid is 'unbalanced',
and basically what happens is that the outgoing sound signal
comes right-on back as an incoming signal.  The reason you
don't notice it using the TDM400P is that the incoming sound
is completely 'in-sync' with you talking through the
handset.  The signal is 'bridged' in the computer, and there
is (basically) zero delay.  Now, when using the X-Lite, the
softphone has to do 'some' processing to get the signal
coming in to the wires (X100P) to your computer speakers.
This processing introduces delay (latency).  Now, you here
your voice (outgoing signal, being 'turned-around' at the
X100P phoneline interface) coming back at you, but with a
more noticable delay.  Hence the echo.  The same effect also
occurs when using SIP hardphones connected to [*] and
calling out over the X100P.
The solution is to implement a 'hybrid balancing' function
at the X100P interface.  Traditioinally for FXO this has
been done in hardware (not flexible) or more recently in
software using embedded DSP chips providing adaptive
real-time hybrid balancing.  The DSP algorithms are not very
complex, and could conceivibly be run on the [*] main
processor.  I have not looked into the codebase, however. 
For a system with only a few FXOs it should not be a real
problem.  
Notice, that a T1 interface is digital, and you do not have
this 'turn-around' issue.
Without looing at the Plantronics design specs, there is no
telling whether it would work.  In any case, the real answer
is to fix the problem right at the X100P interface.
Cheers,
Willy

----- Original Message Follows -----
> Hello all,
> 
> I'm thinking about getting the Plantronics DSP-400 headset
> for use with Xlite softphone.  I currently have a "analog"
> headset that does NOT have a DSP on board, which gives me
> mediocre call quality and echo when talking to the PSTN
> thru my X100P card.  I have zero echo when talking thru my
> X100P on my cordless phones attached to the Digium
> TDM400P.
> 
> Before I got spend the money I was wondering if others
> using USB headsets with a DSP and getting good results? 
> My thought was thought by using a headset with a DSP on
> board the echo would go away?
> 
> Any advice on which USB headset in general to use with a
> softphone?
> 
> Thanks in advance,
> Ed Rubright
> 
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Willy Wouters
ypOne Publishing