AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

In article ,
"Ron Baker, Pluralitas!" wrote:

"isw" wrote in message
...
In article ,
"Ron Baker, Pluralitas!" wrote:


--snippety-snip--

You said you are a physicist/engineer.
What does "linear" mean?

Let's not get too far off the subject here. We were discussing whether
the "tuning beat" that you use to tune a musical instrument involved a
nonlinear process (ie. "modulation").

Then linearity is at the core of the matter.
What does "linear" (or "nonlinear") mean to you?

OK, if you insist -- *in this case* it means "linear enough to not
produce IM products of significant amplitude".

Good enough.
Then spectrum analyzers and the human auditory
system are not linear.
Stay with me here.


I said that it does not, and that
it could be detected by instrumentation which was proveably linear
(i.e.
not "perfectly" linear, because that's not required, but certainly
linear enough to discount the requirement for "modulation").

No nonlinearity is necessary in order to hear
a beat?
Where does the beat come from?

As the phase of the two nearly equal waves move past each other, there
is simple vector summation which varies the amplitude.

Consider two sine waves of precisely the same frequency, where one of
them is adjustable in phase -- use a goniometer, for instance. Use a set
of resistors to sum the two signals, and observe the summing point with
a 'scope or a loudspeaker. By altering the phase of one source, you can
get any amplitude you want from zero up to twice the amplitude of either
one.

Now just twiddle that phase knob around and around as fast as you can.

You've just slightly altered the instantaneous frequency of one of the
generators (but only while you twiddle), and accomplished pretty much
the same effect as listening to the beat between two guitar strings at
nearly zero frequency offset. With no nonlinear processes in sight.

Isaac

You put some effort into that. I give you
credit for that.

The socratic thing isn't working, so here
you go.

I would appreciate it if you would take the time to list *in detail* any
errors in what I wrote. If it "isn't working", I need to know why,
because I don't like to be confused about things.

Is an envelope detector linear? The answer is no.

That's correct, and I'm well aware of it, but so what?

--dissertation on how an envelope detector works snipped--

Do you see how this applies to spectrum analyzers
and the human auditory system?

Sure. But

1) It is possible -- if not practical -- to build a "detectorless" (in
the nonlinear process sense) spectrum analyzer, and

2) None of it is even remotely significant to the subject at hand.

Here it is again: the "beat" one hears when tuning a guitar or other
instrument does *not* require any nonlinear process for its production.
Period.

Isaac

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

In article ,
Jeff Liebermann wrote:

"Bob Myers" hath wroth:

"Ron Baker, Pluralitas!" wrote in message
.. .

No nonlinearity is necessary in order to hear
a beat?
Where does the beat come from?

An audible beat tone is produced by the constructive and destructive
interference between two sound waves in air. Look at a pictorial
representation (in the time domain) of the sum of sine waves,of similar
amplitudes, one at, say, 1000 Hz and the other at 1005, and you'll
see it.

Bob M.

I beg to differ. There's no mixing happening in the air. compression
of air is very linear (Boyles Law or PV=constant).

In general, that's true, but take a look at what happens in the throats
of high-powered horn loudspeakers. You can find info in e.g. "Acoustics"
by Beranek.

Isaac

AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
 

In article ,
"Ron Baker, Pluralitas!" wrote:

--big ol' snip--

When AM is correctly accomplished (a single voiceband signal is
modulated

The questions I posed were not about AM. The
subject could have been viewed as DSB but that
wasn't the specific intent either.

You should take some time to more carefully frame your questions.

Do you understand that a DSB signal *is* AM?

So all the AM broadcasters are wasting money by
generating a carrier?

Of course not. They're saving you (and everybody else) money by allowing
simple receiver designs -- and that was very important in the 1920's.

Isaac

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"Ron Baker, Pluralitas!" wrote in message
...
For the simple reason that there isn't actually a "tone" involved -
in other words, there is no actual signal at the difference frequency.
There can't be, since there is no "mixing" (multiplication) of the
two original tones.

There is no multiplication of 1000 Hz and 1005 Hz
either, is there? Why don't you hear 1000 Hz and
1005 Hz rather than a single tone varying in amplitude?

Because you can't distinguish two tones as separate tones
if they are close enough together in frequency, due to the
way in which the frequency-discrimination process in human
hearing operates.


Could it be that the human auditory system is not
linear?

There are a number of ways in which the human auditory
system is not linear; it's simply that these are not the dominant
cause of the perception of audible "beats."

Bob M.

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

isw hath wroth:

I beg to differ. There's no mixing happening in the air. compression
of air is very linear (Boyles Law or PV=constant).

In general, that's true, but take a look at what happens in the throats
of high-powered horn loudspeakers. You can find info in e.g. "Acoustics"
by Beranek.

Isaac

What am I suppose to look for? I appreciate your recommended research
project, but frankly, I don't care what happens inside a high powered
horn loudspeaker. I prefer to stay fairly on topic about the original
allegation that mixing somehow occurs in open air, which is not true.

Incidentally, if mixing did occur in open air or inside the ear, you
would not be able to comfortably listen to hi-fi music, as all you
would hear would be intermodulation products.

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

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"Jeff Liebermann" wrote in message
...
An audible beat tone is produced by the constructive and destructive
interference between two sound waves in air. Look at a pictorial
representation (in the time domain) of the sum of sine waves,of similar
amplitudes, one at, say, 1000 Hz and the other at 1005, and you'll
see it.

Bob M.

I beg to differ. There's no mixing happening in the air.

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

of air is very linear (Boyles Law or PV=constant). If there were
mixing, you would be able to hear the beat note when one generates two
ultrasonic tones. I belch 25KHz and 26KHz from two transducers, by
our logic, air mixing would create a 1KHz beat note. It doesn't and
you hear nothing.

That was exactly my point. Please read ALL responses I've
made re this topic.

What seems to be the problem here is the model of the human ear is not
what one would assume. It is NOT a broadband detector. The cochlea
cilia (hairs) resonate at individual frequencies. Each one resonantes
at only one frequency (and possibly some sub-harmonics). Therefore,
the human ear model is a collection of narrow band filters and
detectors. Unless the two frequencies involved both cause a single
cilia to simultaneously vibrate at both frequencies, there isn't going
to be any mixing. Each detector can be individually quite non-linear,
but as long as it vibrates at only one frequency, there isn't going to
be any mixing.

This is also a point I noted earlier in this thread.

Bob M.

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"Bob Myers" hath wroth:

"Jeff Liebermann" wrote in message
.. .
An audible beat tone is produced by the constructive and destructive
interference between two sound waves in air. Look at a pictorial
representation (in the time domain) of the sum of sine waves,of similar
amplitudes, one at, say, 1000 Hz and the other at 1005, and you'll
see it.

Bob M.

I beg to differ. There's no mixing happening in the air.

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.

You can demonstrate it to yourself with a suitable audio spectrum
analyzer and tone generators. I recommend "Visual Analyzer 8"
http://digilander.libero.it/hsoft/
Generate two sine waves at any frequencies. Use a cheap microphone to
pickup the audio and display it with the audio SA. You won't see any
sums, differences, or intermodulation products unless you over drive
the microphone or try to produce the tones from a single loudspeaker.

Kindly supply a suitable correction or explanation. I'll gladly
entertain the possibility that I'm wrong.

That was exactly my point. Please read ALL responses I've
made re this topic.

My appologies for not reading all of the 269 posting to this thread.
The thread is a classic case of topic drift. I though I would check
the topic de jure and found your posting.

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

AM electromagnetic waves: 20 KHz modulation frequency on anast...
 

Nobody knows what is beyond our Universe.(I think there is a 100 percent
Vacuum out there, there no end to it) So, do those waves travel out and
into the unknown?
cuhulin

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"Jeff Liebermann" wrote in message
...
isw hath wroth:

I beg to differ. There's no mixing happening in the air. compression
of air is very linear (Boyles Law or PV=constant).

In general, that's true, but take a look at what happens in the throats
of high-powered horn loudspeakers. You can find info in e.g. "Acoustics"
by Beranek.

Isaac

What am I suppose to look for? I appreciate your recommended research
project, but frankly, I don't care what happens inside a high powered
horn loudspeaker. I prefer to stay fairly on topic about the original
allegation that mixing somehow occurs in open air, which is not true.

Incidentally, if mixing did occur in open air or inside the ear, you
would not be able to comfortably listen to hi-fi music, as all you
would hear would be intermodulation products.

Yes everything would become ultra sonici

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"Jeff Liebermann" wrote in message
...
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. You do
HEAR a "beat," however, and that is the result of the amplitude
variation caused by the interference, as noted. 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 have never ever said that "mixing" (multiplication) occurs in air.
If you're going to pick apart what someone is saying, then please
read everything they've said before starting.

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.

Bob M.