752 Chapter 21
is the time an input is kept activated (200 ms) compared
to the decision time taken to activate an input (10 ms).
Access ratio may be readjusted to control the number of
input channels that can activate at one time. Selective
adjustment of the access ratio can also reduce missed
beginnings of words.
21.3.4.7 Automatic Microphone Mixers with Matrix
Mixing to Multiple Outputs
Recent designs in automatic microphone mixers have
introduced matrix mixing to multiple outputs. This fea-
ture allows any input channel to be sent to any number of
output channels and to be sent at different levels depend-
ing on the signal mix desired at the individual output.
The Lectrosonics AM16/12 is a marriage of analog with
digital. All control is accomplished via proprietary soft-
ware that operates on a Windows-based computer. Soft-
ware control allows a 16 in/12 out automatic microphone
mixer with matrix mixing to fit in a two-rack space chas-
sis. The software control also deters unauthorized read-
justment as there are no knobs to twiddle.
Matrix mixing may be used for creating unique
audio feeds for recording, teleconferencing, hearing
assistance, language translation, etc. A courtroom is an
example of a facility where all of these different audio
systems might be required. Matrix mixing also provides
the capability for mix-minus configurations. Simply
put, a mix-minus output signal contains all input chan-
nels except for one or more—i.e., complete mix of all
inputs minus one (or more) undesired inputs. The
mix-minus concept improves gain before feedback. If a
microphone signal does not appear in the closest loud-
speaker, gain before feedback is better than if the micro-
phone signal does appear in that loudspeaker. In a
typical meeting room, talkers do not need to hear their
own voice in the closest loudspeaker. They need to hear
their other talkers located far away from their location.
Mix-minus provides this capability, Fig 21-22.
However, matrix mixing also creates a
problem—how to adjust so many gain variables?
Consider an automatic microphone mixer with twelve
inputs and one output. This mixer requires thirteen gain
controls—one for each input and one for the master
output. Now consider an automatic microphone mixer
with 12 inputs and 8 outputs. This mixer requires 104
gain controls. One hundred four potentiometers and
knobs take up a lot of panel space and are quite expen-
sive. The answer to this problem is control via software.
One example of this design concept is the Lectrosonics
AM16/12.
21.3.4.8 Automatic Mixing ControllerThe Model E-1 Automatic Mixing Controller,
Fig. 21-23, helps professional audio mixers handle mul-
tiple live mics without having to continually ride their
individual faders. This eight-channel signal processor
patches into the input insert points of an audio mixing
console. It detects which mics are being used and makes
fast, transparent cross-fades, freeing the mixer to focus
on balance and sound quality instead of being chained
to the faders. The Model E-1’s voice-controlled cross-
fades track unscripted dialogue perfectly, eliminating
cueing mistakes and late fade-ups while avoiding the
choppy and distracting effects common to noise gates.
Without the need for gating, a natural low-level room
ambience is maintained.
Dugan automatic mixing controllers are used with
multiple live mics and unscripted dialogue including
talk shows, game shows, conference sound reinforce-
ment, houses of worship, dramatic dialogue, wireless
microphones in theaters, and teleconferencing. The
Dugan controllers are typically connected in the insert
points of the console’s mic inputs, Fig. 21-24.
Fig. 21-25 is the block diagram of the E-1 automatic
mixing controller. Each unit handles up to eight chan-
nels, and the units can be linked together to accommo-
date a maximum of 64 mic channels.
The Model E-1 is an eight-channel line-level or
ADAT digital insert device in a half-rack, one unit high
cabinet and has minimal controls. Additional controls
are available via a virtual control panel provided by an
embedded web server. I/O is connected by TRS insert
cables or ADAT optical cables. The Model E can be
linked for up to 64 channels, and it can link with the
Dugan Models D-2 and D-3. Power is 9–24 Vdc or
9–18 Vac.
Three models are available. The Model D-2 has
analog I/O for use in the insert points of analog mixing
consoles. The Model D-3 has AES digital connections
for insertion into digital mixers. Both models feature a
separate control panel that can be placed on the meter
bridge or in front of the console.21.3.4.9 Automatic Microphone Mixers Implemented
in SoftwareIf software can control automatic microphone mixer
hardware, then automatic microphone mixers can also be
completely created in software. This completely digital
approach to automatic microphone mixers can be found
in software based products offered by Allen & Heath,
ASPI, BSS, Crown, Dan Dugan, Gentner, Lectrosonics,