Theatre Design & Technology - Summer 1983 - 20

This would not only increase the possibility of feedback but would also increase ambient noise pickup. It is my
guess that the automatic mixer would
make an unattended (hands-off) system
like this possible whereas it would be unacceptable with a non-automatic mixer.
Still, I caution that I am unaware of
such a system and I emphasize that the
setup would be critical and that the actors' cooperation would be essential.
More Comments From The Consultant
I received some excellent advice on
the use of automatic mixers from the
several consultants I contacted. Farrel
Becker, for example, has used the Industrial Research mixer quite successfully at Wolftrap and in other venues.
Becker says that he often sits at the location of the microphone during a rehearsal to hear what the microphone hears,
a simple but effective technique that
allows him to choose the best microphone positions and to trouble-shoot
things like signal to noise problems.
Dan Dugan, (Dan Dugan Design,
San Francisco) inventor of the Dugan
system automatic mixer, sold by Altec
Lansing, says thal he rarely uses an
automatic mixer in the theatre except for
footlight microphones. Dan notes that
the Dugan/ Altec automatic mixer,
which was designed for speech systems,
is probably not a good choice for music
but works quite well on dialog and
"area" microphones (Ii ke footlight
microphones).
Paul Magil (Paul A. Magil and Associates, Costa Mesa, CA) says that he
designs more showrooms than theatres
but is quite wary of the whole idea of
automatic mixing in the theatre. "If
things were more predictable between
source and microphone," he says, "then
an automatic mixer could work in a
hands-offsiruation." Magil went on to
warn against expecting an automatic
mixer to compensate for the failures of
an inexperienced human operator.
David Klepper (Klepper-MarshallKing, White Plains, Y) agrees with the
idea of caution in the use of automatic
mixers. He warns that the automatic
mixer "can get you into trouble and can
boost the orchestra when you want the
singer on top." Klepper notes, however,
that his associate, Larry King, is now using an automatic mixer, on a trial basis
in a theatre system with apparently satisfactory results.

A Mixed Score
Does the automatic mixer have a
place in the theatre? Yes, sometimes!
Even the experts, however, caution that
it cannot replace the human operator
and can be used effectively only in certain types of applications. My hands-off
example of the dinner theatre system is
purely speculation but represents the
type of controlled situation that would
be needed in a totally automatic system.
The last section of this article is a
brief review of currently available products in case you have the urge to experiment. I was not able to obtain current
information on the JBL automatic mixer and had time only for a telephone
conversation about the IVIE automatic
mixer. Thus, my discussions of these
two products are necessarily limited.
one of these "reviews" is anywhere
near complete. I purposely have covered
only those features that I feel are significant for theatre use.
The Industrial Research "Voice-Matic"
Mixer
(Industrial Research Products, Inc.; Elk
Grove Village, IL)
Like virtually all automatic mixers,
the IRPI "Voice-Matic" mixer was designed for speech purposes. The VoiceMatic was chosen by Farrel Becker for
his theatre systems because it gave him
the ability to bypass the "on/off" feature. The Voice-Matic has many additional features including the ability to
bypass the entire automatic function on
individual channels, the ability to bypass
the "NOM" feature, a low-frequency
roll-off filter, and several options.
One of the IRPI's options, "logic
outputs," is available on many automatic mixers (standard on some). The
logic output feature, in its most simple
form, provides a DC output voltage that
indicates the on or off status of each
microphone. This feature was planned
to allow automatic priority in paging
systems (and other speech system uses)
but might find use in the theatre to
switch tape recorders on and off automatically, for example.
Another IRPI option, the "LevelMatic" master module i an automatic
gain control that raises the level of soft
talker and reduces the level of loud
talker. This action might make the device more suitable for mixing singing
voices or musical instruments. It is not
apparent, however, whether or not this

function would interfere with the
"NOM" feature or whether it might
cause unwanted reduction of the dynamics of a live performance. It would
obviously be valuable in a speech only
system where the primary purpose was
to hear and understand the talkers.)
The Altec Lansing Automatic Mixer
(Altec Lansing; Anaheim, CA)
This is the original automatic microphone mixer and still unique in its operation. The Altec/Dugan automatic mixer does not really turn its microphones
on and off but continuously varies the
level of each microphone from full off
to whatever level the user sets on the
channel volume control. Thus, the term
"threshold" does not really apply. Its
OM reduction feature operates the
same way, that is, a continuous variation of the overall gain depending on
how many microphones are in use and
on the individual gain of each
microphone. Altec calls this "gain sharing" and the result is an automatic mixer that actually mixes.
The equation for this gain sharing is
Ln ,= Ln - [Sum(Ln) - Ln) where Ln I is
the level in an individual channel after
the automatic circuits attenuate that
channel; Ln is the level in the channel
before attenuation and Sum(Ln) is the
sum of the levels in all channels before
attenuation. (All levels are assumed to
be in dB notation.)
In other words, any channel receiving a strong signal will be attenuated
very little, if at all. Any channel receiving a weak signal, or no signal, will be
greatly atten uated or effectively turned
off. This should make the Altec/Dugan
automatic mixer ideal for footlight microphones and it would probably be my
first choice for a hands-off dinner theatre system.
You can modify one channel of the
Altec/Dugan automatic mixer to make
it into an "ambience detection" channel. The microphone connected to that
channel affects the automatic circuitry
but never enters the actual mix (in the
equation, it enters the Sum(Ln) term but
does not reach the audio output of the
mixer). By placing this ambience microphone in the audience, the overall system gain now goes up when audience
noise is low and down when audience
noise is high. This has the effect of
greatly reducing audience noise pickup.
Of course, it also reduces the pickup of
actor's voices but if the actors can be

SITT Summer 1983/Theatre Design & Technology

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