16 Channel Automatic Matrix Mixer
GENERAL TECHNICAL DESCRIPTION
The AM16/12 uses a straightforward analog signal path to provide excellent audio performance. This is coupled with a
sophisticated microcontroller to implement the automatic mixing, matrix control, room combining, and programmable
input and output functions. The Adaptive Level Proportional automatic mixing algorithm is used by the AM16/12. This
algorithm uses the signal level pattern at the microphones to derive a pattern of channel gains. For instance, if only one
microphone channel is being spoken into, its level is dominant and that channel gets most of the system gain, while all
other channels are turned down. If more than one microphone is active, they share system gain according to their
relative levels. A “skewing” function gives some advantage to microphones which are active over time, to minimize
interruptions from transient noise at other microphones. Since the gain of each channel is apportioned continuously
based on its relative level, no abrupt gain changes are made. This makes the automatic action virtually inaudible.
Figure 1 shows the simplified block diagram of the AM16/12. The microphone preamp is a low-noise discrete design,
which is extensively RF protected. The preamp has three gain settings. The 0dB setting allows an input to accept
line level signals, while the +30dB and +50dB gain settings accommodate both low and high sensitivity microphones.
Switchable 15V Phantom power is provided for each channel.
VARIABLE LOW CUT
HIGH CUT/BOOST
TO A/D CONVERTER
MI
X BUS 1
MI
X BUS 2
MI
X BUS 3
MI
X BUS 4
MI
X BUS 5
MI
X BUS 6
MI
X BUS 7
MI
X BUS 8
MI
X BUS 9
MI
X BUS 10
MI
X BUS 11
MI
X BUS 12
MAIN IN
MIX MINUS OUT
Following the mic preamp, the
audio signal passes through a
EXPANSION IN
INPUT #1 (OF 16)
PROCESSOR
CONTROLLED
SWITCH
+15V
AUTO MIX LOG IN
high quality Voltage Controlled
ARRAY
CHANNEL ON
Amplifier (VCA). This VCA,
FROM INPUT 2
FROM INPUT 3
FROM INPUT 4
FROM INPUT 5
FROM INPUT 6
FROM INPUT 7
AUDIO
MIC IN +
VCA
controlled by a signal from the
MAIN OUT
MIC PREAMP
MIC IN -
FROM D/A
FROM INPUT 8
system D/A converter, is used
CONVERTER
MIX MINUS IN
EXPANSION OUT
FROM INPUT 9
FROM INPUT 10
FROM INPUT 11
MIC GND
to implement both static gain
AUTO MIX LOG OUT
FROM INPUT 12
FROM INPUT 13
FROM INPUT 14
TX
FROM INPUT 15
LECNET PORT
FROM INPUT 16
(RS-232)
RX
uC
68HC12
NOM IN 1
PREAMP GAIN
SPEECH
LOG
0dB (LINE)
+30dB (MIC)
FILTER
CONVERTER
control (i.e. mic trim and
+50dB (MIC)
remote input level) and gain
PROGRAMMABLE INPUT 1
PROGRAMMABLE INPUT 2
reduction for the automatic
PROCESSOR
NOM IN 2
PROGRAMMABLE INPUT 3
CONTROLLED
NOM IN 3
VARIABLE
PROGRAMMABLE INPUT 4
1 OF 16
NOM IN 4
RESISTOR
PROGRAMMABLE INPUT 5
A/D
mixing function. A Channel On
NOM IN 5
SERIAL BUS
PROGRAMMABLE INPUT 6
PROCESSOR
PROGRAMMABLE INPUT 7
CONVERTER
NOM IN 6
NOM IN 7
NOM IN 8
NOM TOTAL 1
CONTROLLED
VARIABLE
PROGRAMMABLE INPUT 8
RESISTOR
LED indicates which inputs are
PROGRAMMABLE INPUT 9
PROGRAMMABLE INPUT 10
PROGRAMMABLE INPUT 11
PROGRAMMABLE INPUT 12
PROGRAMMABLE INPUT 13
PROGRAMMABLE INPUT 14
currently active. A sweepable
low-cut filter and a shelving
PROGRAMMABLE INPUT 15
PROGRAMMABLE INPUT 16
AUDIO EXP IN
PROGRAMMABLE INPUT 17
high frequency filter provide
PROGRAMMABLE LOGIC OUTPUT 1
PROGRAMMABLE LOGIC OUTPUT 2
tone control for each input.
PROGRAMMABLE LOGIC OUTPUT 3
PROGRAMMABLE LOGIC OUTPUT 4
PROGRAMMABLE LOGIC OUTPUT 5
NOM TOTAL 2
NOM TOTAL 3
NOM TOTAL 4
D/A
CONVERTER
NOM TOTAL 5
NOM TOTAL 6
NOM TOTAL 7
NOM TOTAL 8
NOM TOTAL 1
NOM TOTAL 2
NOM TOTAL 3
NOM TOTAL 4
NOM TOTAL 5
NOM TOTAL 6
NOM TOTAL 7
NOM TOTAL 8
NOM OUT 1
NOM OUT 2
NOM OUT 3
D/A
NOM OUT 4
AUDIO EXP OUT
NOM OUT 7
NOM OUT 5
NOM OUT 6
CONVERTER
NOM OUT 8
PROGRAMMABLE LOGIC OUTPUT 6
The 16 inputs are routed
8
7
PROGRAMMABLE LOGIC OUTPUT
PROGRAMMABLE LOGIC OUTPUT
PROGRAMMABLE LOGIC OUTPUT 9
through an 18 in / 12 out
PROGRAMMABLE LOGIC OUTPUT 10
PROGRAMMABLE LOGIC OUTPUT 11
PROGRAMMABLE LOGIC OUTPUT 12
crosspoint matrix. The matrix
PROGRAMMABLE LOGIC OUTPUT 13
PROGRAMMABLE LOGIC OUTPUT 14
PROGRAMMABLE LOGIC OUTPUT 15
has multiple crosspoint gains
PROGRAMMABLE LOGIC OUTPUT 16
PROGRAMMABLE LOGIC OUTPUT 17
PROGRAMMABLE LOGIC OUTPUT 18
PROGRAMMABLE LOGIC OUTPUT 19
to accommodate the most
complex signal routing needs.
Aside from the 16 inputs, the matrix also
includes two other inputs: a noise gen
erator and the input signal from the
LecNet Expansion In rear panel connec-
NOISE GENERATOR
tor.
PROCESSOR
CONTROLLED
VARIABLE
RESISTOR
Signals from the Expansion In and
NOISE
BALANCED
10dB
Expansion Out connectors allow easy
LINE OUTPUT 1
SOURCE
LINE OUTPUT
BALANCED
2
10dB
LINE OUTPUT
BALANCED
3
10dB
BALANCED
LINE OUTPUT 4
10dB
BALANCED
10dB
LINE OUTPUT 5
LINE OUTPUT
BALANCED
6
10dB
LINE OUTPUT
BALANCED
7
10dB
LINE OUTPUT
BALANCED
8
10dB
interface to AM8 mixers. In addition, a
Mix Minus signal is available which
allows easy interfacing to teleconferenc
ing hybrids like the TH3A.
An RS-232 port is available to allow
be controlled either by a computer or a
many of the functions of the AM16/12 to
MIC/LINE
BALANCED
10dB
SWITCH
MIC/LINE OUTPUT 9
MIC/LINE
BALANCED
SWITCH
MIC/LINE OUTPUT 10
10dB
dedicated control system (such as the
MIC/LINE
BALANCED
SWITCH
MIC/LINE OUTPUT 11
10dB
AMX
®
or Crestron™ systems).
SWITCH
MIC/LINE OUTPUT
MIC/LINE
BALANCED
12
10dB
PROCESSOR
CONTROLLED
ATTENUATORS
AM16/12 Block Diagram
Rio Rancho, NM – USA
3
