AKG AS 8 User manual

AS8/AS8TC
8 Channel Automatic Matrix Mixer
OPERATING INSTRUCTIONS
and trouble- hooting guide

INTRODUCTION
The AKG AS8 Automatic Microphone Mixer is an 8 channel, single rack space audio mixer. Using the unique Adaptive
evel Proportional mixing algorithm, the automatic action is inaudible and simple to set up. The AS8 offers remote control
of all channel levels and the master level. In addition, a sophisticated compressor/ leveller is included for dynamic range
control of the audio program material. The AS8 has an RS-232 port for remote setup or control by a computer or other RS-
232 compatible controller. More than one AS8 may be coupled together when applications call for more than 8 channels.
TABLE OF CONTENTS
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
GENERA TECHNICA DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
INSTA ATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
FRONT PANE DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
REAR PANE DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
FCC PART 15 NOTICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
OPERATING INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
REMOTE EVE CONNECTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
TROUB ESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
SERVICE AND REPAIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
RETURNING UNITS FOR REPAIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
SERIA CAB E WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
AMX CAB E WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
AMX Programming Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
SERIA PORT COMMANDS AVAI AB E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
WARRANTY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Back cover
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GENERAL TECHNICAL DESCRIPTION
The AS8 uses a straightforward analog signal path to provide excellent audio performance. This is coupled with a
sophisticated microcontroller to implement both the automatic mixing and the compressor/leveller algorithms. The
Adaptive evel Proportional automatic mixing algorithm is used by the AS8. 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 each channels’ gain is apportioned continuously based on its relative level, no abrupt gain changes are made. This
makes the automatic action virtually inaudible.
The Compressor/ eveller function uses a combination of the short-term and long-term signal dynamics to determine the
optimum amount of gain reduction in any situation. The effect of the function is to control both the average program level
(for consistent long-term sound system level) and to minimize any large short-term deviations. The gain reduction function
is gated, which means that there are no noise ups associated with program signal pauses.
Figure 1 shows the simplified block diagram of the AS8. 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. 15V Phantom power
is provided for each channel, and is switchable. In addition, each channel may be switched into either the Direct (always
on) or Auto mode.
Following the Channel evel control, the audio signal passes through a high quality Voltage Controlled Amplifier (VCA).
This VCA, controlled by a signal from the system D/A converter, is used to implement gain control for the automatic mixing
function, as well as the remote level function. A Channel On ED indicates which channels are currently active.
Signals from the Expansion In and Expansion Out connectors allow multiple AS8 mixers to be combined if more than 8
channels are necessary for the application. In addition, a Mix Minus signal is available which allows easy interfacing to
teleconferencing hybrids.
An RS-232 port is available to allow many of the functions of the AS8 to be controlled either by a computer or a dedicated
control system (such as the AMX or Crestron systems).
DIRECT/AUTO
PHANTOM POWER
+5V
+15V
TO uP
Remote Level CH1
Remote Level CH2
Remote Level CH3
Remote Level CH4
Remote Level CH5
Remote Level CH
Remote Level CH7
Remote Level CH8
Remote Level Master
Auto Mix Log In
Compressor/
Leveller
Threshold
From CH1 –
From CH2 –
From CH3 –
From CH4 –
From CH5 –
From CH –
From CH7 –
From CH8 –
To CH1 –
To CH2 –
To CH3 –
To CH4 –
To CH5 –
To CH –
To CH7 –
To CH8 –
Dir/Auto CH1 –
Dir/Auto CH2 –
Dir/Auto CH3 –
Dir/Auto CH4 –
Dir/Auto CH5 –
Dir/Auto CH –
Dir/Auto CH7 –
Dir/Auto CH8 –
Compressor/Leveller
Gain Reduction Display
12 dB
9 dB
dB
3 dB
SERIAL
EEPROM
8HC705
uC
D/A
CONV
A/D
CONV
A/D
CONV
SPEECH
FILTER
LOG
CONVERTER
Tone Control
AS8-TC Only
MIC
PREAMP
PREAMP
GAIN
0 dB (LINE)
+30 dB (MIC)
+50 dB (MIC)
CHANNEL LEVEL AUDIO
VCA
TO A/D
CONVERTER
FROM
OTHER
CHANNELS
MAIN IN 1
MIX MINUS OUT 2
AUTO MIX 3
LOG IN
MAIN OUT 1
MIX MINUS IN 2
AUTO MIX 3
LOG OUT
Σ
ΣΣ
EXPANSION
IN
EXPANSION
OUT
MAIN
OUTPUT
RS-232 OUT
RS-232 IN
SERIAL DATA LINK
DIR OUT
MIC IN +
MIC IN -
MIC GND
HI LO
MAIN
LEVEL
CHAN
ON
1 OF 8 INPUT CHANNELS
AS8 BLOCK DIAGRAM

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INSTALLATION
Installing the AS8 properly is simple, and only requires attention to a few issues. The AS8 should be used in a grounded
metal rack. If only one AS8 is being used, it should be placed in the Master mode, using the rear panel switch. Erratic
performance will result if the unit is in the Slave mode, but no damage will be done to the unit. Proper operation will be
restored when the unit is switched to the Master mode. If multiple AS8s are used together, the first AS8 (i.e. the one with
Expansion In port used but not the Expansion Out port) should be switched to the Master mode, while all other AS8s should
be in the Slave mode. Figure 2 shows the correct interconnection for multiple AS8s.
Microphone connections should be made with good quality braid or foil shielded twisted pair. The shield should be used for
the ground (Pin 1) connection. If an unbalanced signal is used, the unbalanced signal lead should be connected to the “+”
input terminal, while the unbalanced ground lead should be connected to both the “-” and ground terminals of the input
connector.
Output connections to the Main Out connector can be made balanced or unbalanced. If an unbalanced connection is
desired, simply connect the unbalanced signal lead to the “+” output terminal, and the unbalanced ground lead to the
output ground terminal. eave the “-” output terminal unconnected.
Access to the Remote evel Control port is accomplished using the DB-15 connector (supplied).
INTERCONNECTING MULTIPLE AS8s
Master
Slave
Slave
Switch in
MASTER Position
Switch in
SLAVE Position
Switch in
SLAVE Position

FRONT PANEL DESCRIPTION
CHANNEL SECTION
CHANNEL LEVEL - Controls the relative signal level of each channel. Normal operation of the Channel evel control is
from about the 10 o’clock position to the 2 o’clock position.
CHANNEL ON LED - Gives an indication as to which channels are active.
LF - (TC version only) Adjusts the low frequency response of the channel.
HF - (TC version only) Adjusts the high frequency response of the channel.
MAIN SECTION
MAIN LEVEL - Controls the overall output level of the AS8. If multiple AS8s are used together, only the Main evel control
of the last (i.e. Master) AS8 will be operational.
COMPRESSOR/LEVELLER IN/OUT - Enables or disables the compressor/leveller function.
COMPRESSOR/LEVELLER THRESHOLD - Sets the signal level above which the Compressor/leveller is active. Note
that the Threshold level is measured before the Main evel control. This means that adjustments of the Main evel control
will not affect the amount of gain reduction.
COMPRESSOR/LEVELLER GAIN REDUCTION METER - Shows the instantaneous amount of gain reduction applied
by the compressor/leveller system.
AS8 FRONT PANEL
AS8TC FRONT PANEL
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