"Picture the largest loudspeaker in the universe sitting outside"
"Now add to that signal a small, high pitched, low amplitude waveform"

I couldn't of put it better myself. I was watching the argument and
watching it turn into a slanging match. I wish that wouldn't happen.
The only problem as far as I could see is that Porky was thinking of
just a singular frequency, rather than a high frequency "riding" a low
frequency.

When that occurs, the train and whistle analogy indeed seems to make
sense. With a singular frequency, IMHO, it does not.

Cheers,

Mark.
--

PenguiN wrote:
Picture the largest loudspeaker in the universe sitting outside
somewhere. It's so big that it has a maximal excursion of several
feet. Now picture a very low bass signal played on that speaker at
almost maximal volume. The speaker cone is vibrating
in-out-in-out-in-out.

Now add to that signal a small, high pitched, low amplitude waveform.
The two waveforms are added together so that it seems like the higher
pitched wave is "riding on top of" the bass wave. As far as our
super-excursion speaker is concerned, the location that's generating
the high pitched sound is moving forward and backward several feet.