[AG-TECH] interesting slashdot .. software echo cancellation

Michael Gay mngay at purdue.edu
Thu May 9 08:21:42 CDT 2002

The Gentners, ASPIs and others are expensive because they are 
small/niche market items.  I do beleive this will go down as the 
technology becomes less expensive and development costs are 

Software echo cancellation is really an interesting term because it 
actually is all software!  The difference is the platform the code runs 
on, either an embedded DSP processor or a PC platform.  The 
embedded device or "appliance" device uses a DSP chip, which is 
simply a microprocessor optimized for the implimentation of DSP 
algorithms.  Typically these use what is know as Harvard 
Architecture which can perform multiple operations during one 
clock cycle.  Pentiums are based on the Von Neuman 
architecture.  This architecture is not optimized for performing real 
time digital signal processing, but accomplishes the task using 
brute force (lots of horsepower and CPU cycles).  

This is comparable to how a sleek sprots car with a 6 cylinder 
engine could outrun a tractor-trailer semi rig with a much larger and 
more powerful engine.  The semi must pull a lot more to go the 
same distance  but can haul a variety of things while the sports car 
was built for speed and hauling only one thing...from which I shall 
refrain from typing on a public list.

For beginners in DSP, I have written a paper which you can access 


It was written with broadcast engineers in mind and speaks mostly 
of audio compression rather than echo cancellation, but a lot of the 
basic premises are the same.  I also focus more on embedded 
"appliance" DSP because I am an embedded programmer more-so 
than a PC programmer.  Any DSP veterans out there are welsome 
to correct any gross innacuracies which might have eluded me.  
Also, for those who want to see the rest fo the site, pardon the fact 
that the web site has not been updated in some time.  Real work 
always seems to get in the way.

Now that I have bored you all to tears, back to PC echo 
For small venues, I see no reason why some smart PC 
programmer out there in the AG community could not write a 
multichannel echo canceller and take advantage of the six audio 
channels used as standard input for the AG audio encoder.  This 
would allow five to six echo cancelled channels without the use of 
an outboard canceller.  Not practical for a large room system but 
such a method could be more inline with a small venue budget.

On 8 May 2002, at 15:19, Jay Beavers wrote:
> Actually, software echo cancellation, automatic gain control, and noise
> reduction is already in Windows XP and used in the Windows Messenger
> conferencing app.
> However, once you enter AG-like scenarios with multiple microphones,
> large spaces, and audio processing you're in a specialized, small market
> that is well served by Gentner et al.
>  - jcb
> -----Original Message-----
> http://slashdot.org/askslashdot/02/05/07/2241246.shtml?tid=99
> Is anyone working on such a thing?  The gentners are expensive pieces of
> equipment...
> -asher

Michael Gay
Purdue University
Manager, Engineering Services
Division of Instructional Services
1092 Stewart Center
W. Lafayette, IN 47907
765 494 5100
"I am always doing that which I can not do, 
in order that I may learn how to do it." 
                            - Pablo Picasso

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