Subject: Re: Echo Cancellers

From: "Hari Krishna Vuppaladhadiam" <[email-masked]>
Date: Thu, 27 Apr 2000 14:23:41 -0700

A typical chain like this:

Telephone ==> Central Office  ==> Gateway ==> Internet ==> Gateway ==>
Central office ==> Telephone

Can we consider a telephone itself as a Hybrid device? If so does it require
an EC?
The central office where Hybrid conversion takes place need to have an EC!
Does the Gateway require an EC if the central office already has one?
I somehow did not see companies seriously discussing Acoustic Echo
canceller!

Say if Residential Gateway is designed then is there a necessity of an EC?
(if not why?)

May I request someone to clear my doubts.

Regards
Hari

---

From: George Michaelson <[email-masked]>
Date: Fri, 28 Apr 2000 12:11:16 +1000

We just (re)deployed an ATM/AAL5 layered videowall with subb 100ms end-to-end
delay in the network (IP measure, other payload same medium) and also some ISDN
(>100ms) and IP (variable)

Back about 5 years ago, decent audio/hw with echo cancelling built in was
bloody expensive. I recall Van discussing this in terms of the complexity
of the models which have to try and deal with an 'average' size room and
the kinds of echo you can get, and how badly cheap phone 'handsfree' echo
cancellation works (If you've been on a multiway call recently you will
know this I am sure. it has a long baseline mute/volume behaviour which
stinks, and one person typing on a keyboard which is not voice data, in
a very specific part of the sound spectrum, and damn loud can wipe out any
echo canceller I've used).

We looked again just a few weeks ago. a unit designed to plug into a VideoConf
unit is still around $700-$1000 $AU. same for a PC plugin unit.

a non-echo cancelling senheisser mike is still around $1000. Use something
for $25 from Tandy, and it can work. But its really horses for courses.

Decent audio gear comes at a premium. I doubt if the chipcount in these
devices is very high, or in real compute terms the complexity is very
high given FPGAs or even a PC-on-a-card to deal with it.

The market expectation is that you sell few of them, and charge a lot for it.
  
If somebody wants to invest a lifetime, writing some code to model this stuff
so I can dial into VAT or some other app "My room is 25M**2 and I appear to
have a wall delay echo of 5ms, and a keyboard near to the mike and want it
to not unmute mike but do want speech to turn it on, with minimal clipping"
would be sweet. Right now, our $750 unit sends my cohort tapping his foot
against the table as a deep throbbing drum in the middle of conversations and
the speaking is so 'bright' it almost rings.

cheers
	-George
--
George Michaelson         |  DSTC Pty Ltd
Email: [email-masked]    |  University of Qld 4072
Phone: +61 7 3365 4310    |  Australia
  Fax: +61 7 3365 4311    |  http://www.dstc.edu.au