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

[Jason A. Pattie]

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willy at yponeinc.com wrote:
| 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.

I have been fighting this very thing from the moment we implemented our
system.  Our original goal was to connect to the Asterisk box through
VPN tunnel connections and access the X100P interface card to receive
and make incoming and outgoing calls from wherever we happened to be (at
home, in the office, etc.).  However, the echo situation is still not
satisfactory on software phones.  I've got the echo cancellation tuned
to what I think is the best it's going to get without major improvement
in the algorithms.  Would a realtime kernel help in this regard?

BTW, there are echo cancelling algorithms available in the zaptel code.

| 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

If you are wanting the Plantronics to do echo cancellation, it's
probably not going to do that except for noise cancelling at the
microphone input.  I doubt it will do the kind of echo cancellation you
are desiring on its own.  At least I don't see anything in the Windows
tray icon that would give me this functionality.

| is to fix the problem right at the X100P interface.

I agree, which is what the echo cancelling algorithms are for in the
zaptel drivers.  They just don't seem to work 100%, yet.

| 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?

I routinely use the Plantronics DSP 400 (mostly with IAX softphones),
even under Linux.  The latest version of ALSA 1.3c fixed all my
problems.  It now works wonderfully with gnophone even.  Now I can use
it under Linux, not just Windows anymore, which makes me very happy.

- --
Jason A. Pattie
pattieja at xperienceinc.com
Xperience, Inc. (http://www.xperienceinc.com)
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