[Freeswitch-users] Removing echo.

Sean Devoy sdevoy at bizfocused.com
Tue Mar 19 21:12:49 MSK 2013 

Anthony and Spencer,

 

Thanks for your responses. Anthony the megaphone analogy really worked for
me.  Spencer thanks for saving me the time of looking up those settings.

 

I agree cell phones frequently have huge echo.  The longer the echo delay
(aka higher latency) the harder it is to correct makes perfect sense as
well.

 

I actually had a chance to talk to one of the users experiencing this
problem.  Bear in mind I usually get to talk to her boss who is looking for
reasons to not pay his bill.  She said they do still "occasionally" get echo
but it is not too bad.  She said it is always worse when the call certain
people (that correlate's with end user device problems).  Then she mentioned
I was one of the ones they usually get echo with and it was happening now,
but not that bad!

 

Opportunity knocked, so I jumped in!  First a quick note of reference - I
have moderately high hearing loss and wear hearing aids.  I keep my headset
turned up fairly high!  I asked the user who called me to talk to herself
while I did some tests and tell me if the echo got better or even went away.
Low and Behold - mute made it go away COMPLETELY.  As much as I hate it when
Anthony is right, it is hard to deny it.  I tested further and each of these
things helped enough that she noticed:  Turning my headset speaker down on
the inline volume control, turning the headset speaker down at the phone,
turning my microphone boost down (this headset has 3 settings for microphone
level), muting at the phone or on the inline headset control.  All of those
things taken collectively say "Listen to Anthony butthead."

 

So, assuming the cause of the echo is beyond my control (e.g. someone else's
phone) are we just screwed or is it just cost prohibitive?  I would rather
reply that it would cost $5000 to fix it than say "can't be helped."

 

Suppose the user detects bad echo.  Is there anything we could do (assuming
they could notify FS through a programmable key or even web link, etc)?
Could we drop the gain to and from the remote end?

 

I promise to let this die now.  Let me here your final thoughts.

 

Thanks again for your time and patience.

 

From: freeswitch-users-bounces at lists.freeswitch.org
[mailto:freeswitch-users-bounces at lists.freeswitch.org] On Behalf Of Spencer
Thomason
Sent: Tuesday, March 19, 2013 11:40 AM
To: FreeSWITCH Users Help
Subject: Re: [Freeswitch-users] Removing echo.

 

Hi Sean,

We were experiencing a similar problem with these units and were able to
verify that it was in fact the remote end but the threshold of the echo
canceler seems to be too low by default.  We could hear echo and then unplug
the handset from the base on the other end, without muting, and the echo
would stop.  We found that decreasing the gain slightly all but eliminated
complaints.  This does reduce the level slightly but in our traces it was
close to on par with an analog handset.  The pertinent configuration options
are:

 

  <Handset_Input_Gain>-6</Handset_Input_Gain>
  <Headset_Input_Gain>-6</Headset_Input_Gain>
  <Speakerphone_Input_Gain>-6</Speakerphone_Input_Gain>
  <Handset_Additional_Input_Gain>0</Handset_Additional_Input_Gain>
  <Headset_Additional_Input_Gain>0</Headset_Additional_Input_Gain>
  <Speakerphone_Additional_Input_Gain>0</Speakerphone_Additional_Input_Gain>

 

Thanks,

Spencer

 

 

On Mar 19, 2013, at 7:49 AM, Anthony Minessale wrote:





Sean,

 

You are welcome to disagree.  Science is driven by people being unwilling to
accept things as they are.

I do have some explanations for you if you are interested.

 

Cisco and Linksys ATA both have echo cancelers in them at the point where
the analog data is converted to digital.  This is the ideal place for it as
I mentioned earlier.  So they actually are doing something about the problem
and that is why you do not observe one.  Getting echo while using a cell
phone is also very common.  The more latency and conversion of the audio
data you experience, the more likely you can have echo.  (iPhone is
notorious) The other place where its important to have echo cancellation is
the point where the digital data in the rtp stream is transferred into the
TDM gateway interfacing with the PSTN.  This is why most TDM cards like
Digium and Sangoma have onboard echo canceler chips.  We are not completely
helpless, we can do some unnatural things like decode the audio signal we
are passing through and try to run some echo cancellation on it but, in the
conditions you describe where you hear a perfect replica of what you are
saying 2-5 seconds later only softer.  That is for sure outside the range of
any echo canceler.  It cannot reliably tell that this clean signal coming
many seconds later should be filtered out because its a replica of data that
has already passed by long before.  Usually in this type of issue, you are
actually hearing the other side hear what you said.  So you say the
statement, the latency takes its toll and the echo is coming back at you
from the far end as they are hearing it.  

 

I am open to options.  We do have some work on doing some inline audio
processing underway but we should not rely on them if we can possibly
control the surroundings better first.  If you are talking to me in the same
room using a megaphone and I am wearing ear plugs.  Its easier to tell you
to turn off the megaphone and tell me to remove the ear plugs.

 

 

 

 

On Mon, Mar 18, 2013 at 9:24 PM, Sean Devoy <sdevoy at bizfocused.com> wrote:

Hey Anthony,

 

Does that mean PBXMate is not worth investigating?

 

I have to disagree here. Placing the blame entirely on the phones at the
other end doesn't hold water for me.  I have had echo problems calling from
my cell phone when leaving a voice mail on FS where there is no phone at the
other end. So clearly there are situations where it ain't just the phone at
the other end.  It also leaves no explanation why Cisco Phones and Linksys
ATAs don't have the same problem with Commercial Venders like Vonage.  They
don't have anything different at the end of the line for echo cancellation
then FS does. I have also had users confirm they are still getting echo with
the microphone MUTED on my end.

 

Again, I love FS and I am not trying to bash anyone or any code.  I am just
saying there has to be more to this puzzle.  I know what a crappy speaker
phone's echo sounds like and I am not at all concerned about that. Crappy
speaker phones sound like crappy speaker phones no matter what. I don't
think that's what I am trying to track down.  These are business call where
90% are using the standard handset on business quality phones.  It happens
at various levels, but when it is at the bad end of the spectrum (e.g. long
delay and loud), it does not sound like echo off of walls coming back in a
microphone.  It is like my input channel has been delayed, softened and
looped directly back to me crystal clear.  Maybe it is one of my VOIP
providers' hardware or software and is load dependent, but the problem
exists outside of cheap phones. And of course it is only reproducible on 3
calls in a hundred at peak usage hours, making it a nightmare to track or
diagnose.  But those 3 calls are the ones my customers want to talk about at
billing time.

 

Now, I have just thrown that all out there is hopes that 50 people will say
"That absolutely never happens to me with FS" so I can look at it a
different way.

 

Thanks for your thoughts.

Sean

 

From: freeswitch-users-bounces at lists.freeswitch.org
[mailto:freeswitch-users-bounces at lists.freeswitch.org] On Behalf Of Anthony
Minessale
Sent: Monday, March 18, 2013 7:30 PM


To: FreeSWITCH Users Help
Subject: Re: [Freeswitch-users] Removing echo.

 

 

The best place for echo cancelation is in the clients as close to the mic as
possible.

Someone asked why skype and some apps are better.  It's because they have
echo cans in the client app.

Sip soft phones are basically toys unless they have some kind of advanced
gain and echo controls on your pc because that is where your mic is and
could have the vol turned up too high etc.

 

>From FS perspective in the middle, we can't tell its echo or not because we
are just passing the data along and we're typically getting it 30-70 ms too
late.  

 

 

In general, you don't get echo when using real phones because they have
proper hardware and software to deal with the place where the audio is being
sampled and rendered.

 

 

 

 

 

On Mon, Mar 18, 2013 at 5:15 PM, Christopher Rienzo <cmrienzo at gmail.com>
wrote:

Echo cancellation is not easy.  The only open source one I've seen is GPL
(making it license incompatible with FreeSWITCH) and is not suitable for
handling echo over IP networks.  Perhaps tricks are being played using VAD
to only allow only one speaker at a time in the ooVoo conference?

 

On Mon, Mar 18, 2013 at 5:53 PM, Mimiko <vbvbrj at gmail.com> wrote:

Today we tried ooVoo conference system with theirs client using same
boxes and microphones - again, no echo. How this can be? Is it only
commercial products have echo removing function?


--
Mimiko desu.

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-- 
Anthony Minessale II

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FreeSWITCH Developer Conference
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