"Scott Dorsey" wrote in message
...
The original Audimax/Volumax combination had no phase rotator. I
worked
at an AM station that used them, and the chief engineer had installed a
phase reverse switch on the announcer mike and auditioned each
announcer
to tell them which position to use. (Apparently they had used figure-8
mikes a year or so before I got there, and the announcers just used the
front or back of the mikes).

A lot of stations using the Audimax/Volumax would also have a phase
rotator in the chain, though. CRL made a popular one, and so did
Garron.
Some folks made some boards that dropped inside the Volumax for it too,
but I never used any of those. I went to the Optimod as soon as I
could,
and it has a great phase rotator.

The phase rotator is a hell of a great gadget, it gives you a lot of
loudness
without any perceived distortion. Mind you, for communications
applications
it's no more effective just than aggressive clipping, but there are
folks
who don't want aggressive clipping.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."


Thanks for the corrections, Scott.

Aggressive clipping creates a ton of distortion unless the voice signal
is split into several bands, each processed and filtered, and then
combined. The phase rotator theoretically produces no amplitude
distortion, and due to the way the human ear works, the shifting of the
phases is not heard. I read once that the cochlea and its nerves
perform physiologically something akin to a mathematician performing a
Fourier analysis. I find it amazing that we process sound, for the most
part, on the amplitude versus frequency information, and ignore the phase
versus frequency information.

With modern operational amplifiers, it is fairly simple to produce a good
phase rotator using cascaded all-pass networks. I would hate to have to
manufacture the original SymmetraPeak with its inductor-capacitor network
lattices.

Well, we are pretty far from the original subject, but I have enjoyed the
discussion. However I do have a Boatanchor question.

I remember seeing ads in QST in the 1960's for a device I think was
called "Echoplex." It was supposedly used on commercial and military
voice communications circuits. I never heard one of these in use by a
ham, probably because their cost could buy several Collins S-Line
stations. Doing a Google search brings up lots of echo-effects
processors for guitars and such, but I found nothing for communication
usage. Do any readers here remember the device and its manufacturer and
how it worked?

73, Barry WA4VZQ