What is modulation?
It's a fairly basic phenomenon, it happens in physical systems all the time. It has something to do with carrying something (that has a scientific name, a specific, exact sort of thing).

What gets carried? How does modulation carry something? What does it have to do with entropy?

I guess no-one knows. Or maybe nobody has read this post yet.

So, nobody, what do you think modulation is? Is it important? Do we need an understanding of it (whatever it might be), or is it something that "just happens", so no worries?

I guess no-one knows. Or maybe nobody has read this post yet.

So, nobody, what do you think modulation is? Is it important? Do we need an understanding of it (whatever it might be), or is it something that "just happens", so no worries?

I just now found this thread.

Modulation is what carries the intelligence in a signal. It can be a modulated EM wave, water wave, Indian/ boy scout smoke signal and scores of other things.

It really has no connection to entropy but the signal being modulated certainly does. The term "modulating" simply means changing from a steady- state to a varying state.

Where are you headed with this?

I'd say the description you just posted begins to explain what modulation (the carrying, or sending of information, say), actually is.

It's a broader term than the realm of signalling, but then, it is signalling, or discriminating, a signal. A signal is really just information. Modulation is variation, but what actually varies? Why or how does it vary?

What about what the word meant originally (to sing, make, or set to music)?

Meaning is something that gets modulated, too.
But meaning is disjoint from the scientific view of information--just a random arrangement of equivalent bits.

You're sure entropy doesn't come into modulation itself? What about information entropy, or relaxation? You mean the carrier itself doesn't change energy, or entropy?

I'd say the description you just posted begins to explain what modulation (the carrying, or sending of information, say), actually is.

It's a broader term than the realm of signalling, but then, it is signalling, or discriminating, a signal. A signal is really just information. Modulation is variation, but what actually varies? Why or how does it vary?

In the way the term modulation is normally used, electronics and radio for example, the signal is simply energy and is not carrying any information. Only when the signal is modulated (modified) does it carry information. A radio carrier wave is nothing more than an energy broadcast but it can be modulated by intrerruption (as in Morse Code transmission) or the intensity or frequency of the carrier can be made to vary in accordance with information being imposed on it.

What about what the word meant originally (to sing, make, or set to music)? That's still quite valid and applies in exactly the same way as my example above. In the case of singing the airstream leaving the throat and mouth is modified (modulated) causing it to carry information - just as speaking is a form of modulation of the same airstream.

[quote]You're sure entropy doesn't come into modulation itself? What about information entropy, or relaxation? You mean the carrier itself doesn't change energy, or entropy?

Modulation, in and of itself, is not related to entropy. The carrier - be it a radio carrier, stream of air, current of water, electrical current, whatever - is, however. It's the carrier that is transporting energy from a higher level to a lower one (the simple meaning of entropy) and not the modulation.

Modulation is entrainment of harmonic motion, SHM or CHM?
Is entanglement a kind of modulation, too?

Information "entropy" confuses things a bit, seeing as it's also little to do with physical entropy, or dispersal.

OK, so looking at an ocean wave (something everyone who's seen the ocean probably knows about).

These things move along in some direction, and carry momentum. They perturb the medium (the ocean): the surface moves vertically as a momentum wave passes horizontally across it.

They're produced by wind usually (or by submarine earthquakes, subsidence, and geologic/tectonic displacements), and maintained by gravity(? they're a gravity wave), they eventually run out of water, and "collapse" on to land somewhere.

The surface of a liquid can maintain other kinds of wave, too, because of tension (the interface between a liquid and another phase of matter), and non-linear forces like friction and shear.

Surfers use their weight (inertia) and the surface tension of a board that's less dense than ocean water, to harness, or transfer momentum from a wave to themselves.

So surfers are the "intelligence" carried, or modulated, by an ocean wave. Surfers are wave signals (so are sealed bottles with rolled-up bits of paper inside, or any object, like a dead whale, that ocean waves can entrain)

Friction and shear forces are also involved, but the surfer can use their weight to entrain their own momentum, in a kind of feedback, to the wave, and build their own speed (by surfing back up the wave). This is the same kind of thing you can do on a swing rope, or that any child knows about who has used a swing.

OK, so looking at an ocean wave (something everyone who's seen the ocean probably knows about).

These things move along in some direction, and carry momentum. They perturb the medium (the ocean): the surface moves vertically as a momentum wave passes horizontally across it.

They're produced by wind usually (or by submarine earthquakes, subsidence, and geologic/tectonic displacements), and maintained by gravity(? they're a gravity wave), they eventually run out of water, and "collapse" on to land somewhere.

The surface of a liquid can maintain other kinds of wave, too, because of tension (the interface between a liquid and another phase of matter), and non-linear forces like friction and shear.

Yes, and...?

Surfers use their weight (inertia) and the surface tension of a board that's less dense than ocean water, to harness, or transfer momentum from a wave to themselves.

So surfers are the "intelligence" carried, or modulated, by an ocean wave. Surfers are wave signals (so are sealed bottles with rolled-up bits of paper inside, or any object, like a dead whale, that ocean waves can entrain)

Stated backwards, actually. The ocean wave is modulated by the intelligence/information it carries - NOT the other way around. There are also several other modulators that inject information into waves that arrive at landfall. You mentioned a few in the post before this one and there's also the wake produced by ship movements, distant storms, etc.

There's a few of us here that are very familiar with the principles of modulation (and demodulation, for that matter) - but my question is simply this: where are you heading with this discussion? What point needs to be made?

Is there a point that needs to be made? OK.

Can you explain your point about the ocean wave being modulated by the surfer? Is it accurate to say that a surfer uses feedback the way I described it? Can you describe the terms modulate, and carrier a bit more succinctly? You've stated that the carrier is energy, and the modulation is what carries the information, or signal.

P.S. I know what a FFT is (I've written one in Fortran V). I minored in Physics, and I understand the e^st surface, and frequency response (of a circuit or channel).
Information comes down channels, and it's supposed to have (conditional) entropy. Many claim that information is non-physical, and doesn't have any physical meaning. However, all the entropy equations I've come across (including Shannon's and equivalents) are mathematically symmetrical. Is there a good explanation for this symmetry?

P.S. when a wave moves a surface object, like a small boat, does the boat modulate the (vertical) wave motion, or is the vertical surface displacement the modulation itself?
i.e. the momentum-wave modulates the medium (by perturbing its surface)?
If the latter, why doesn't the wave modulate a surface object (which is arguably part of the medium its "in" or on)? Why is this back to front, as you state?

IOW, is a displacement, or pertubation, of a medium, a modulation, as well as a harmonic motion?
HM is to do with the transfer, or commutation, of energy in all its forms. It's periodic, or wavelike.

So is a motion a thing that moves things (a force), or is it the thing that is moved (by the force)? Is it active or passive?