[asterisk-users] [headset/mic] Volume too low + echo in * (Gilles)

[Dave Platt]

> 
> Different brand/model, but similar as they are both el cheapo,
> entry-level headsets. I tried using them on a laptop, and I get
> marginally better microphone output, even with its volume cranked all
> the way up + automatic gain control enabled.
> 
> I guess those on-board soundcards by Realtek aren't as good as a
> quality microphones. I'll get a USB headset instead and see how it
> goes.

It does sound as if the mic-input gain is too low for those
headsets.

> Right after the connexion is made between the PC with the headset and
> a Siemens IP phone located on the same LAN. Both are using SIP. It's
> light, but a bit noticeable. I'll try again with a USB headset and see
> if it goes away.

Hmmm.  The traditional cause of echo on analog phone lines is
the presence of impedance mismatches... the electrical signal
"reflects" when it hits a point where the impedance of the
transmission line changes, and returns to the origin (where it
is heard as an echo).

This situation really shouldn't exist at all, in the digital
stages of transmission (i.e. between the SIP endpoints).  The
causes would have to lie elsewhere.

One source of echo I've observed on SIP calls in the past is
purely acoustic... cheap handsets/headsets.  It's possible
for acoustic feedback to occur within such a device... the
microphone picks up a fraction of the sound being generated
by the speaker/earpiece, and is transmitted back towards the
point of origin.  I had this problem with a cheap little
USB handset I use here at work... its case is mostly hollow,
and channeled sound from the speaker to the mic.  When I
called my wife and home she complained of hearing her voice
echoing.  I opened the handset, stuffed the open areas with
cotton wadding, and added a few small pieces of left-over
car-door-damping sticky-sheet to the inside of the case.
Problem gone - no more echo.

So, once again, you may be having a headset/handset-related
problem!

> I noticed, something, though: While I only kept G11u on both the XLite
> and Siemens, I noticed that sound coming from the Siemens contains
> some reverb when running Asterisk (1.4.4) on an Atcom appliance
> (www.atcom.cn/IP01.html), while the reverb is gone when running
> Asterisk (1.6.2.5) on a regular PC with Ubuntu. I guess codecs sound a
> bit different depending on what hardware they're running on.

That's odd... the U-law codec is about as simple and deterministic
as it gets, and really shouldn't have an effect on any echo behavior.

Is it possible that "silence detection" settings were different in
these cases?  If a phone endpoint was configured to detect "silence"
and stop sending RTP audio packets, it could have the side effect
of suppressing low-level acoustic echo occurring within the phone
handset/headset, since the level of this would fall below the
silence-detection threshold.

> Thanks much for the education  :-) 

Quite welcome!