Thank you for the clarification. it was the Hyperbolic nature that was
getting me, but your right that hyperbolas look pretty straight for this
application.

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On Thu, 16 Sep 1999, John Hallam wrote:

> On Thu, 16 Sep 1999, Dag Bakken wrote:
>
> > LGJ> I have a question about this whole concept. Are you detecting
> > LGJ> sounds which are a fixed distance away, in this case i have no
> > LGJ> problem. However, how will you be able to detect the angle of the
> > LGJ> source when you have no distance information?
> >
> > Well...  An angle/direction doesn't need distance information.
> > [ ... snip ... ]
>
>         This is almost right.  The time difference measured at the
> microphones is directly related to the difference in path length between
> source -> left microphone and source -> right microphone.  In 2
> dimensions, the set of points whose distances from two fixed points (foci)
> differ by a constant is a hyperbola;  in 3 dimensions, the surface you
> need results from spinning the hyperbola around the axis of the sensor
> system.
>
>         What people normally do is (a) ignore elevation and assume the
> sound source is in the azimuthal plane and (b) assume the source is far
> enough away that the hyperbola looks like a straight line.  For many
> applications these two approximations, while strictly false, are perfectly
> acceptable.
>
> John Hallam.
> Senior Lecturer, School of Artificial Intelligence,
> Division of Informatics, University of Edinburgh,
> Scotland.
>