The basic math of TDOA-only (time-difference-of-arrival) localization
was covered in my freshman calculus book.  Since I don't have it handy,
and I can't recall it from memory, I would just say look for a TDOA
reference in any good book on electromagnetics.  The topic is much more
seriously covered in a passive radar context than in acoustics.
Although, Haykin's book on array DSP is a good one, and has some very
relevant stuff.  Look for array processing books as they will generally
have a more directly applicable mathematical context to your problem
than most other approaches.  The sonar DSP folks worry about this
problem a lot.

Also, as mentioned above, you need three or more microphones to resolve
the ambiguity inherent in 2-microphone setups.  I prefer 12-16
microphones for my array setups, although I have gotten by with as few
as 8 in a pinch.  Matlab handles the data processing well, although I
use CoolEdit (now Adobe Audition) for the data acquisition.  Doing it
in real time requires a multithreaded approach and more than one CPU,
or alternatively, an FPGA.  There are lots of cheap and/or free
programs to use for data acquisition.  You must get one that does
seamless recording to hard drive (most do this no problem), not just
one that records into memory, since those have to compete with other
programs that will be consuming memory as well.  There really are very
few of the latter about anyway.

For more than 2 channels of PC audio data acquisition, you will
definitely need a multichannel audio card.  Event/Echo, M-Audio, MOTU,
etc. all make fine cards.  Look at your local Guitar Center in the Pro
Audio section for some help.  They have plenty of good setups for not
too much money.  Some of the cards have a breakout box that includes
pre-amps for each channel.

Someone mentioned reverberations above.  Given enough microphones, the
reflections can be sorted out easily, until the number of reflections
exceed the degrees of freedom of the array.  Start off working on an
open football pitch or park (not a stadium) so as to minimise these
during testing.  Once you've got that sorted out, move to a more
complex reverberant environment.  Good luck.

Cheers,
Rob

P L U M ! wrote:
> Hi everyone,
> I'm back.
> This time i need to suggest some books on "Acoustics" to purchase for
> our library here.
> Particularly related to Sound Localization.
> Can anyone suggest some good books?
> 

the canonical text is probably:

3-D Sound For Virtual Reality and Multimedia
Durand R Begault, AP Professionalm, ISBN 0-12-084735-3
(NB: expresses a very strong preference for headphone reporoduction, hence 
devotes much space to HRTFs)

A good general text is:

Acoustics and Psychoacoustics
David M Howard, James Angus, (2nd Ed. 2001)
Focal Press, ISBN 0-240-51609-5

and also from Focal Press:

Spatial Audio
Francis Rumsey (2001)
ISBN 0-240-51623-0

I also suggest yuu post this question to the sursound mailing list. Several top 
engineers, acousticians and surround-sound specialists are active there.

These books also include bibliographies, from which you should be able to 
identify more specialized/scientific texts as you need.

Richard Dobson

Hi everyone,
I'm back.
This time i need to suggest some books on "Acoustics" to purchase for
our library here.
Particularly related to Sound Localization.
Can anyone suggest some good books?

Hi everyone,
I'm back.
This time i need to suggest some books on "Acoustics" to purchase for
our library here.
Particularly related to Sound Localization.
Can anyone suggest some good books?

karthik.ravikanti@gmail.com (Plum) wrote:

>Hi, I'm working on a semester project on sound source localization,
>where my aim is to determine the position of the source of a sound
>using  two microphones and estimating the time delay of arrival. But,
>how do I process the signals from the two microphones???
>I mean how do I send the two signals to a PC???
>Say i add the two siganls....ow do  i separate them then?

Bruel & Kjaer ( sp? Danish company ) has done a lot of work in this
area.  You might see if they have literature available.


( modify address for return mail )

www.numbersusa.com
www.americanpatrol.com

Thanx a lot Mr.Dobson, that really helped....I have Audacity here...and
will use it.
Thanx a lot everyone.

"ETS" <emale80919@yahoo.com> wrote in message
news:10r1j965n5ruh3c@corp.supernews.com...
> Plum wrote:
> > Hi, I'm working on a semester project on sound source localization,
> > where my aim is to determine the position of the source of a sound
> > using  two microphones and estimating the time delay of arrival. But,
> > how do I process the signals from the two microphones???
> > I mean how do I send the two signals to a PC???
> > Say i add the two siganls....ow do  i separate them then?
>
>
> You record them as wav files if you like.  Matlab will read them in.
> look up "wavread" command.  If it's stereo, it will read in a 2D signal
> array so you process the 2 channels from there.  If it's mono, it
> returns a 1D array.  A good place to look for information on
> localization is:
>
> http://www-engr.sjsu.edu/~duda/Duda.Research.frameset.html
>
> Tim

You can only find the bearing with two mics and even that is  not unique as
the sound has the same delay (assuming you have polarity!) both in front and
behind the two mixs. You can tell bearing and whether the sound is coming
from the left or right of course.
You will also have trouble estimating time-delay as cross correlation only
works well for white noise signals and you will have reverberations too.

Tom

"P L U M !" <karthik.ravikanti@gmail.com> wrote in message news:<1102103073.714970.140290@c13g2000cwb.googlegroups.com>...
> Mr. Bernsee,
> What do you mean by line signal??
> Can you please consider this to be some sort of tutorial and elaborate
> on that?
> Also, after sending it to the PC sound card, how do i get the sampled
> data?
> Do i record it in the form of a wav file?
> And then the very first question....how do i then separate the two
> channels???
> Coz, the PC sound card has only one Mic input....
> Also can u suggest any open source libraries for processing wave
> files???
> Or can i process them using matlab???

Maybe if you provide a bit more information on your overall
requirements it will make the answers easier.

For example, is this a 'real time' practical system you're trying to
build? or can you get away with just proving the concept?  Answering
that will answer most of your questions for you.

As Stephan mentioned, take a look at preamps, you can get a cheap one
for around $60.

QN

Richard Dobson wrote:

> [SNIP]
> 
> I don't use Matlab (not a student, can't afford it); as far as I know it 
> has functions for reading and writing soundfiles into vectors for use 
> with the full gallimaufry of Matlab functions. Others on this list will 
> be able to tell you much more about that.
> 
> [SNIP]

Scilab [ http://scilabsoft.inria.fr/ ] can read/write mono/stereo WAV 
files and do any math you wish on resulting vector(s).

Price is right --- FREE.

There is an active newsgroup [ comp.soft-sys.math.scilab ] with helpful 
individuals. Time delay of responses can be erratic at times. But replys 
can definitely be worth waiting for.

[ For prescriptive grammarians -- apologies participle dangling for ;]