Using TDM400's here and I have tried everything to cure the echo. I have used the Milliwatt test from the telco and from asterisk to tune RX/TX gain via a patched ztmonitor. What happens is I experience midcall echo. I turned on aggressive_suppressor and it seems to do great. The problem happens with misc. noise around the office will cause it to mute the other end of a phone call while they are talking. I haven't been able to find anywhere in the MEC2 source to limit when it mutes the remote party. It seems to do it with just the slightest bit of sound coming from the room. What are my options besides getting mad and ordering a PRI and a TE100? -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.digium.com/pipermail/asterisk-users/attachments/20050307/2e7f6e15/attachment.htm
On March 7, 2005 01:23 pm, Dennis Webb wrote:> Using TDM400's here and I have tried everything to cure the echo. I > have used the Milliwatt test from the telco and from asterisk to tune > RX/TX gain via a patched ztmonitor. What happens is I experience > midcall echo. I turned on aggressive_suppressor and it seems to do > great. The problem happens with misc. noise around the office will > cause it to mute the other end of a phone call while they are talking. > I haven't been able to find anywhere in the MEC2 source to limit when it > mutes the remote party. It seems to do it with just the slightest bit > of sound coming from the room. What are my options besides getting mad > and ordering a PRI and a TE100?PRI and TE110 won't save you; we've had echo issues with our TE405P and a Bell Canada PRI. All the PRI does is ensure *you* are not causing echo. Now I'm curious -- What physical phones are on either side of this call? Do you have a speakerphone on? I've never heard of an echo canceller acting how you describe, but lots of speakerphones do exactly that. -A.
The style of echo canceller in use in MEC2 cannot cope with both echoed sound
and 'new' sounds coming down the pipe at the same time (double talk).
Accordingly it has to stop certain parts of the processing during the so called
event. Once double talk has been 'detected' the echo can is frozen for
at least DEFAULT_HANGT samples (the default is 600 samples = 75ms). Put another
way, the echo can stays frozen at least 75ms _after_ the end of detectable
double talk - known variously as the 'holdover' or 'hangover'
timer. The AGGRESSIVE_HCNTR on the other hand causes the echo can tracking to
kick back in _before_ the holdover timer has expired (default 160 samples =
20ms). In addition, enabling the 'aggressive suppression' option also
changes the math around subtraction of the echo model from the signal resulting
in stronger suppression at the cost of more noticable distortion on low-echo
calls.
You can find a fairly detailed reference implementation of the same algorithm
in:
Messerschmitt, David; Hedberg, David; Cole, Christopher; Haoui, Amine; Winship,
Peter; "Digital Voice Echo Canceller with a TMS32020", in Digital
Signal Processing Applications with the TMS320 Family, pp. 415-437, Texas
Instruments, Inc., 1986.
A pdf of which is available by searching on the quoted document title at
http://www.ti.com/
I would suggest experimenting with (raising) the value of MIN_UPDATE_THRESH_I if
you're getting unsupressed echo. My understanding is that this represents
the minimum reference signal power estimate level that will cause filter
adaptation. If this is too low relative to the signals coming off the T1 then
background noise can cause the filter coefficients to constantly be updated and
the echo can to 'diverge'.
I suspect the problems people have are to do with digital pad being added to the
signal somewhere that pushes the signal floor out of range of the fixed
constants that this implementation uses - hence people who have success from
fiddling with the channel gain parameters. I've got a sneaking suspicion its
Central Office related - perhaps some vendors switches correct for pad before
putting digital signals out to the customer? We're hooked to a Lucent GTD5
remote office and I've had bad, but extremely inconsistent echo problems
with both analog and digital 1B channels regardless of where the far end is -
down the road or across the country. I've heard of others doing VoIP on the
same model switch with similar problems.
I've put quite a few tens of hours into understanding MEC2 and I'm still
nowhere near all the way there. Getting input on this kind of thing from people
with the CO engineering experience gets difficult... I'll be honest here -
we coughed up for some an old mid 1980s Tellabs 2531 hardware echo cans off of
eBay and they did a 100% better job than any of the software cans provided with
Asterisk. Wierdly that Tellabs still has issues with some calls (particularly
with loud background noise) but upgrading to a newer 2572 64ms unit pretty much
took care of that too. Regardless, do not underestimate the damage unresolved
echo can do to the viability of a VoIP project.
Hope that helps.
Kris Boutilier
-----Original Message-----
From: Dennis Webb [mailto:dwebb@delta-express.cc]
Sent: Monday, March 07, 2005 10:51 AM
To: Asterisk Users Mailing List - Non-Commercial Discussion
Subject: Re: [Asterisk-Users] Tweaking AGGRESSIVE_SUPPRESSOR
This seems to be how AGGRESSIVE_SUPPRESSOR works. To make sure you don't
get echo, it does what a speakerphone does, mute the other party if it hears
audio from your end. There is a setting in mec2_const.h for
AGGRESSIVE_HCNTR=160 that says in the comments 20ms, I'm assuming this is to
tell how long to suppress the other party. There is nothing on this that I have
found anywhere and since we are live, I can't change until later to see how
it works.
{clip}
This may be of some use to you on your quest: http://bugs.digium.com/bug_view_page.php?bug_id=0002820> -----Original Message----- > From: Kris Boutilier > Sent: Tuesday, March 08, 2005 2:01 AM > To: dwebb@delta-express.cc; Asterisk Users Mailing List - > Non-Commercial > Discussion > Subject: RE: [Asterisk-Users] Tweaking AGGRESSIVE_SUPPRESSOR > > > The style of echo canceller in use in MEC2 cannot cope with{clip}> > -----Original Message----- > From: Dennis Webb [mailto:dwebb@delta-express.cc] > Sent: Monday, March 07, 2005 10:51 AM > To: Asterisk Users Mailing List - Non-Commercial Discussion > Subject: Re: [Asterisk-Users] Tweaking AGGRESSIVE_SUPPRESSOR > > > This seems to be how AGGRESSIVE_SUPPRESSOR works. To make > sure you don't get echo, it does what a speakerphone does, > mute the other party if it hears audio from your end. There > is a setting in mec2_const.h for AGGRESSIVE_HCNTR=160 that > says in the comments 20ms, I'm assuming this is to tell how > long to suppress the other party. There is nothing on this > that I have found anywhere and since we are live, I can't > change until later to see how it works. > {clip} > >
>Wierdly that Tellabs still has issues with some calls (particularly withloud background noise)>but upgrading to a newer 2572 64ms unit pretty much took care of that too.ah yes the old 2571/2572 trick, where you able to find sources for the 2 port chassis & power supply ? the 2571, 2572 cards are easy to find
> -----Original Message----- > From: TC [mailto:trclark@shaw.ca] > Sent: Tuesday, March 08, 2005 9:35 AM > To: Asterisk Users Mailing List - Non-Commercial Discussion > Subject: Re: [Asterisk-Users] Tweaking AGGRESSIVE_SUPPRESSOR > > > >Wierdly that Tellabs still has issues with some calls (particularly with loud background noise) > >but upgrading to a newer 2572 64ms unit pretty much took care of that too. > > ah yes the old 2571/2572 trick, where you able to find sources for the 2 > port chassis & power supply ? the 2571, 2572 cards are easy to find >Actually an eight slot wire-wrap chassis came with the 2531's and they're pin-compatible with the 257x cards. I took it home and went to town on it with an angle grinder and tig welder and, voila, four two-slot chassis. As for power supplies, eBay provided them also - a bunch of DIN rail mount 48vdc supplies from industrial instrumentation - these cards require less than 1 amp each to operate. If others were considering deploying these cards in desperation they could just as easily have cabling soldered directly to the card edge connector seeing as they're all 1/8" pads. You'd only need to connect approximatly 10 wires - Send IN & OUT, Receive IN & OUT and +/-48vdc. Demonstrating an effective, successful echo cancellation system would probably be enough to loosen the purse strings enough to cough up for an 'offical' chassis. I can post edge-connector pinouts and wiring instructions to the wiki if there is interest. Kris Boutilier
> -----Original Message----- > From: Kris Boutilier > Sent: Wednesday, March 09, 2005 10:56 AM > To: Asterisk Users Mailing List - Non-Commercial Discussion > Subject: RE: [Asterisk-Users] Tweaking AGGRESSIVE_SUPPRESSOR > > > > -----Original Message----- > > From: TC [mailto:trclark@shaw.ca] > > Sent: Tuesday, March 08, 2005 9:35 AM > > To: Asterisk Users Mailing List - Non-Commercial Discussion > > Subject: Re: [Asterisk-Users] Tweaking AGGRESSIVE_SUPPRESSOR > > > > > > >Wierdly that Tellabs still has issues with some calls > (particularly with loud background noise) > > >but upgrading to a newer 2572 64ms unit pretty much took > care of that too. > > > > ah yes the old 2571/2572 trick, where you able to find > sources for the 2 > > port chassis & power supply ? the 2571, 2572 cards are easy to find > > >{clip}> > I can post edge-connector pinouts and wiring instructions to > the wiki if there is interest. >There is an as-yet incomplete draft up at http://www.voip-info.org/tiki-index.php?page=Tellabs+Hardware+Echo+Cancellers . Comments/questions/editorial assistance appreaciated. Kris.