From: "Greg" <gfreitag@x??x.xxxx
Date: Fri Nov 19, 1999 2:32 am
Subject: Re: new article
>From: Dan Nelson <dprimary@e...>
>My mistake, I was combining ITD gap and Haas effect into the Haas
>effect. Do you have any insights into ITD gap and the Haas effect?
A fairly good definition can be found at:
http://www.rane.com/par-h.htm
If we look at the example of two speakers with a mono source our
brains produce a phantom source in the middle. If we start adding
delay to one of the speakers the center image will begin to shift to
the undelayed speaker. At some point (about 20ms) the delay will
be great enough that the sound will now appear to be coming only
from the undelayed speaker. As everybody knows it is also possible
to shift the phantom image by changing the level of one of the two
speakers through the use of a pan pot or balance control.
So it is possible to shift the apparent source of the image by:
1) Using short time delays
2) Level differences between the two sources
An early reflection can be thought of as a separate speaker delayed in
time. If we imagine an ideal situation where the reflecting surface
has an absorption coefficient of 0, (100% reflective), and also
imagine a speaker that has uniform polar response, in other words
the off axis response is the same as the on axis response. Since the
reflected sound would be identical to the sound produced by the
speaker, we would now hear a phantom source some place
between the two sources. In the real world the spectral response
of the reflections will not be the same as that of the speaker on axis
for two reasons:
1) The off axis response vs. frequency of the speaker will not be the
same as the on axis response.
2) The absorption coefficient of the reflecting surface vs. frequency
will vary.
The ratio of the direct to reflected sound is now frequency dependent
and our perception of the location of the sound becomes dependent
on the frequencies involved. The complex sounds we listen to are
composed of many frequencies which appear smeared between the
the speaker and the reflected image.
Greg