> 1) Could these phase differences possibly occur on such a minute
> scale and at such a rapid rate that the resulting "flanging" or
> "wavy" effect is almost imperceptible to most people?
Curt,
Our ears cannot hear phase differences on continuing sounds between
left and right, only transients with different timings. But, and a big
but, if you mix left and right with a time or phase difference you
will generate flanging. This mixing can take place at any stage but if
it is in playback loudpeakers, you could then hear the effect which
might not be audible on headphones.
> 2) Would your explanation accommodate the observable fact that
> introducing boundaries/baffles into the picture almost always
> stabilizes the image, eliminating the effect?
Boundaries, baffles, reflectors, all tend to boost sounds arrving at
right angles, but this can quickly become too conplex to analyse. The
fallback from difficult theory is what you hear with your ears.
> 3) Any thoughts on how this anomaly occurs in M-S arrays?
Yes. From the front, M-S arrays give a very good stereo image for
sound objects up to the angle where the rising S signal becomes lower
than the (usually) falling M signal. Beyond that angle, including
vertical pickups, the derived left and right signals get out of phase.
You can widen the "sweet" pickup area by decreasing the S signal, but
at some point, and at the rear of the rig, left and right will go out
of phase.
I said above that we can't hear phase on continuing sounds, but in
this case we can hear out of phase transients clearly, especially in
headphones. Try it. If you reverse the phase of left or right, the
back of the M-S pair becomes the sweet spot.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
|