Hi Cameron,
 Since this aural exciter before the Dolby chain has been going on, I
just checked with www.dolby.com and found this there:
"Phase Correctors" and Dolby Surround
                                By Jim Hilson
                           Surround Broadcast Engineer
                      Dolby Laboratories Licensing Corporation
Since the introduction of stereo broadcasting, devices designed to
correct the phase of audio signals have been in existence. Their
original use was to be for replacing the azimuth adjustment on tape
machines used to "cart" commercials for radio stations. Since the phase
on submitted tapes was and still is prone to be different on each tape,
a unit such as this could save countless hours of machine alignment.
Using this device would make the carts "sound better."
As broadcasters became aware of these units, their place at the station
took a new location. They started appearing at the input to the
transmitter as a "catch all" because in addition to their ability to
correct small phase errors found on tapes, they could correct and fix an
out of phase condition. Using this device would mean that any out of
phase signal would be corrected and all the mono viewers would hear the
information.
Sounds like a good idea, but it isn't. Unfortunately, the units aren't
smart enough to detect when signals should and should not be out of
phase. For example, signals thatare present in a proper Dolby Surround
mix may contain conditions where there is more out of phase information
than in phase information. A perfect example is a front to back pan. As
the effect passes the half way point it begins to contain more out of
phase information than in phase information. When doing live
sporting events, a large crown roar with announcers talking over the
ambiance could suddenly have more out of phase than in phase information
if the announcers were to simply stop talking. When these conditions
occur the unit will momentarily flip the phase until the situation
returns to "normal." The return flip usually has a small delay before
taking place. Depending on how you are listening will determine what you
actually hear.
In Dolby Surround, the center and surround channels will be reversed,
the announcers will begin talking from the surround speakers. In stereo,
little will be noticed, although the mix will appear to have a "hole" in
the middle. In mono, the announcers will be totally gone. Of course,
this will only last a second or two so you will hear the signals
bouncing around the room in surround or miss words if you are listening
in mono. These conditions usually prompt those irate phone calls from
your viewers.
While the use of a phase corrector may make sense as an automatic
azimuth adjuster, the use as a "catch all" for improper engineering
and/or attention to detail can and will actually cause more harm
than good where Dolby Surround encoded shows and material are being
played.
Dolby Surround is now being used for more than just movies.
Approximately 20 weekly or daily TV shows are routinely using Dolby
Surround as are several recording artists making CD's and cassettes.
Live concert broadcasts are also being looked at favorably by
radio stations and more and more commercials are being produced, but not
necessarily marked as Dolby Surround encoded.
Having the Dolby Surround encoded signals pass properly through your TV
or radio station is our number one concern. If you must have a phase
corrector in the line, may we suggest that you make the phase flip
function an operator actuated function. Have the unit trigger an alarm
when an out of phase condition occurs and let the operator decide if the
signal is truly out of phase or just has a large content of out of phase
material present.
                         © 1996 Dolby Laboratories, Inc.
Aural exciters and "spatializers" fall into the same catagory as these
broadcast phase correctors. At least, here is the word of mouth from
those that designed Dolby in the first place. While their site is
primarily professional audio oriented, there are some interesting
articles on surround sound, and setting up systems that anyone with a
home theatre surround system may find useful.
 Bonnie *:>
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