[Phil]

Joseph Meditz wrote:

Phil Allison wrote:

"Andre Jute"


Let's hear some more about this dynamic phase shift that pours a pint
of vinegar into a Crown preamp.


** Dynamic phase shifting of audio signals is all around us, all the time.
The fact that cones move, continuously alters the origin and hence time of
arrival of any higher frequencies being simultaneously radiated. Phase
shift in degrees ( at any point in time) is simply 360 x cone excursion /
wavelength of the high frequency.

Some call this effect " Doppler Distortion" - a misnomer.



Hi Phil,

Here's my take on this interesting topic.

I say that this is precisely an acoustical frequency modulator. If you
input two sinusoids, one low and one high, then the spectrum of the
upper one will be spread out about its center. And the greater the
amplitude of the bass signal, the greater the modulation index. From
the modulation index one could predict what the side bands will look
like.

I found the term "Doppler Distortion" helpful. The situation here is
not exactly like the sound of the horn of a train passing a station.
Rather, it is the sound of the horn of a crazy train oscillating back
and forth across the station.

Joe

So, is an acoustical frequency modulator some type of equipment? It does
sound like what I *think* Otala is saying happens when a feedback amp
gets hold of two sinusoids, as you say. What is a good methos for seeing
this spread? Someone suggested (oh hell, I think it was Arny; a USEFUL
idea???) using a spectrum analyzer, maybe it's that simple?

By the way, I *think* PA is wrong, in a way. It may be that a cone
moving forward at a bass frequency can Doppler shift a high frequency
signal, but doesn't the mic that recorded the two frequncies to begin
with invert this process, thereby cancelling it out? Just thinking ...

Phil