Rich Grise hath wroth:

On Wed, 11 Jul 2007 22:52:17 -0700, Jeff Liebermann wrote:

"NotMe" hath wroth:

(Please learn to trim quotations)

Actually the human ear can detect a beat note down to a few cycles.

No, you cannot. Figure on 20Hz to 20KHz for human hearing:
http://hypertextbook.com/facts/2003/ChrisDAmbrose.shtml

What happens when you zero beat something is that your brain is filling in
the missing frequencies. As you tune across the frequency, and the beat
note goes down in frequency, most people overshoot to the other side, and
then compensate by splitting the different.

No, you've got it all wrong.

Sorry, I'm perfect and never make misteaks.

The beat note happens because, when the
signals are close to 180 degrees out of phase, they cancel out such that
there is, in fact, no sound. This is what your ear detects. Now, if
you're zero-beating, say, 400 Hz against 401 Hz, I don't know if the
801 Hz component is audible or if it's even really there, but
mathematically, it kinda has to, doesn't it?

Ok, I'll bite. I think you'll find that if you actually do that with
a non-distorting audio mixer[1], and look at an oscilloscope, you'll
see the 1Hz envelope, but the 400 and 401 Hz tones will still be
there. Same on a spectrum analyzer, where the two carriers (400/401)
are still there. If they're there, you'll hear them. The tones may
be going up and down once per second (1Hz), but you'll still hear
tones in between. No way are they going to disappear with a 1Hz
separation. However, if they're exactly on the same frequency, and
exactly 180 degrees otto phase, they will cancel.

The zero beat example I offered is more a psychology problem than
acoustics or hearing. Our ears and brain expect the sweep through
zero beat to be continuous, that we fill in the missing frequencies.
It's really apparent in ham radio, where tuning across carriers is a
common event. I've watched how people do it, and noticed that they
always overshoot and come back to the perceived center. If you ask
them to nail the frequency to within 10Hz without overshooting, they
usually have a difficult time.

[1] no compression, limiting, fuzz box, reverb, equalizer, etc.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558