"Bob Myers" hath wroth:


"Jeff Liebermann" wrote in message
news
Nor did I say there was. The phenomenon of interference
between two compression waves in a given medium is not
an example of "mixing."

You didn't say that. You that a beat note would be produced. From
your posting at:
http://groups.google.com/group/sci.electronics.basics/msg/f18c6dfefbd55a82
"An audible beat tone is produced by the constructive and
destructive interference between two sound waves in air."

That's wrong. There's no audible beat note produced in the air.

Sigh - which, again, is as I explained it further on. I said that
there is no actual component at the "beat" frequency.

So, there's no "component" of the "beat" frequency. Well, in my
limited knowledge of what the term "beat" means in RF circuitry, it's
normally used in the context of a multiplicative mixing function, such
as BFO (beat frequency oscillator). Is there some other way to create
a "beat" frequency other than multiplicative (mixing)? I don't know
of any.

Also, what's a "component" of the beat frequency? Is that just one of
the numerous N*F1 +/- M*F1 multiplicative mixer products?

You do
HEAR a "beat," however, and that is the result of the amplitude
variation caused by the interference, as noted.

Interesting. So, using my original example, if I take two ultrasonic
tones, above human hearing, you suggest that I do *HEAR* a beat, but
that there's no actual component at the beat frequency. The does
present a problem because if this is true, then the mixing has to
occurring somewhere in order for my brain to detect the beat
frequency. Is it mixing in my ear, in the cochlea, in the nerves
going to the brain, or in the brain somewhere? I don't think it's any
of these because when I do this experiment, I don't hear any such beat
note.

I'm also having a problem with your use of the term interference. In
the present context, I would presume this to be something involving
interferometer or quantum wave mechanics. I guess I've been out of
the broadcast business for too long.

I did manage to find a nifty Java applet that shows the effects of
acoustic interference:
http://falstad.com/interference/
It appears to refer to variations in amplitude across the area where
both tones are present. What's missing is any reference to any beat
note. Certainly additive mixing is present as this is what causes the
variations in amplitude. However, I don't see any reference to "beat"
notes in any of the articles explaining audio interference phenomenon.
You cannot hear
the beat effect (I won't use the word "tone" here, which I admit
was a possible source of confusion in the original wording) if the
two original tones are too far apart, simply because you can only
perceive such amplitude variations if they occur below a certain
rate.

I'll make it easy. The difference of the two tones are in the audible
range. For example, 25KHz and 26KHz to produce a 1KHz beat note. The
amplitude component is certainly there as you demonstrated with your
explanation of audio "interference". So, do I hear the 1KHz, or don't
I hear the 1KHz? If I hear it, where does the mixing occur?

I have never ever said that "mixing" (multiplication) occurs in air.
"An audible beat tone is produced by the constructive and
destructive interference between two sound waves in air."
How else are you going to produce an *audible* beat note except by
multiplicative mixing?

Actually, I have an issue with only one word in the above quotation.
It's not audible. Drop that word and it's mostly correct.

If you're going to pick apart what someone is saying, then please
read everything they've said before starting.

Actually I did. I read most of the 270 odd articles in this thread,
but I ignored any that were obviously a waste of time, such as those
consisting of massive quotation with one line of worthless drivel
added.

And whether or not you READ all the postings in a thread is one
thing - whether or not you choose to respond to a given posting
out of its context is something else entirely.

Are my comments really out of context? I had issues with much of what
was said in this thread. Never mind the topic drift and inane
responses. I resisted temptation and did not respond to any of these
until someone, in this case you, went off what I consider to be the
deep end. I did not question your qualifications, did not send you
off on some reading adventure, and addressed your specific statements
directly, as I'm doing in this reply.

However, I can do it your way. Your previous reply reeks of
blustering and I would advise you cease and desist.



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