Audio Technica SmartMixer AT-MX381 User manual

AT-MX381 SmartMixer®
8 Channel Automatic Mixer

Important Safety Instructions
1) Read these instructions.
2) Keep these instructions.
3) Heed all warnings.
4) Follow all instructions.
5) Do not use this apparatus near water.
6) Clean only with dry cloth.
7) Do not block any ventilation openings. Install in accordance with the man-
ufacturer’s instructions.
8) Do not install near any heat sources such as radiators, heat registers,
stoves, or other apparatus (including amplifiers) that produce heat.
9) Do not defeat the safety purpose of the polarized or grounding-type plug.
A polarized plug has two blades with one wider than the other. A ground-
ing type plug has two blades and a third grounding prong. The wide blade
or the third prong are provided for your safety. If the provided plug does
not fit into your outlet, consult an electrician for replacement of the obso-
lete outlet.
10) Protect the power cord from being walked on or pinched particularly at
plugs, convenience receptacles, and the point where they exit from the
apparatus.
11) Only use attachments/accessories specified by the manufacturer.
12) Use only with the cart, stand, tripod, bracket, or table
specified by the manufacturer, or sold with the appara-
tus. When a cart is used, use caution when moving the
cart/apparatus combination to avoid injury from tip-over.
13) Unplug this apparatus during lightning storms or when
unused for long periods of time.
14) Refer all servicing to qualified service personnel. Servicing is required
when the apparatus has been damaged in any way, such as power-sup-
ply cord or plug is damaged, liquid has been spilled or objects have fallen
into the apparatus, the apparatus has been exposed to rain or moisture,
does not operate normally, or has been dropped.
Notice
The apparatus shall not be exposed to dripping or splashing and that no
objects filled with liquids, such as vases, shall be placed on the apparatus.
Use with Rack Mounting
If you install the unit into a rack, select the rack having an all-pole mains
switch (with a contact separation of at least 3mm in each pole) in its front.
In case of emergency, turn off the mains switch on the rack, or disconnect the
plug of the rack quickly.
About Power Cord
This model does not include AC power cord.
Therefore, you have to purchase it at your local store.
You can confirm it at “ Power Cord List ”.
Power Cord List
Caution
Warning
To prevent fire or shock hazard, do not expose the unit to rain or moisture.
To avoid electrical shock, do not open the cabinet. Refer servicing to qualified
personnel only.
Safety Cautions
Prior to use of this product, review all safety markings and instructions.
Warning: This apparatus must be grounded.
This product is a safety class 1 product. There must be an uninterruptible safe-
ty earth ground from the main power source to the product’s AC input.
Whenever it is likely that the protection has been impaired, disconnect the
power cord until the ground has been restored.
Installation place
Please install this model in the place where ventilation is good.
Caution for FCC
You are cautioned that any changes or modifications not expressly approved in
this manual could void your authority to operate this equipment.
Warning for FCC
This equipment has been tested and found to comply with the limits for a Class B
digital device, pursuant to Part 15 of the FCC Rules. These limits are designed to
provide reasonable protection against harmful interference in a residential
installation. This equipment generates, uses, and can radiate radio frequency
energy and, if not installed and used in accordance with the instructions, may
cause harmful interference to radio communications. However, there is no guar-
antee that interference will not occur in a particular installation. If this equipment
does cause harmful interference to radio or television reception, which can be
determined by turning the equipment off and on, the user is encouraged to try to
correct the interference by one or more of the following measures:
—Reorient or relocate the receiving antenna.
—Increase the separation between the equipment and receiver.
—Connect the equipment into an outlet on a circuit different from that to
which the receiver is connected.
—Consult the dealer or an experienced radio/TV technician for help.
IC statement
This Class B digital apparatus complies with Canadian ICES-003.
Cet appareil numérique de la classe B est conforme á la norme NMB-003 du
Canada.
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
CAUTION: TO REDUCE THE RISK OF ELECTRIC SHOCK,
DO NOT REMOVE COVER (OR BACK)
NO USER-SERVICEABLE PARTS INSIDE
REFER SERVICING TO QUALIFIED SERVICE PERSONNEL
The lightning flash with arrowhead symbol within an equilateral
triangle is intended to alert the user to the presence of
uninsulated "dangerous voltage" within the product's enclosure
that may be of sufficient magnitude to constitute a risk of
electric shock to persons.
The exclamation point within an equilateral triangle is intended to
alert the user to the presence of important operating and
maintenance (servicing) instructions in the literature
accompanying the product.
8 Channel Automatic Mixer
Installation and Operation
Manufacturer Parts No. Electrical Rating Approval No. Country
H.R.SILVINE-CMC Co., LTD. CAT-009
N.M. SVT
EF-28
50/60Hz,
125V,
10A
U.S.A
Canada
Plug: UL (E69228) CSA (LL93534)
Cord: UL (E69167) CSA (LL97391)
Connector: UL (E69228)
CSA (LL93534)
Kawasaki Electric Wire
Co., LTD. KP-610 H05VV-F
KS-31A
50/60Hz,
250V,
10A
UK
Plug: BSI (KM14544)
Cord: Demko (95-0272/95117)
Connector: Demko
(98-01458/124208)
Kawasaki Electric Wire
Co., LTD. KP-4819D H05VV-F
KS-31A
50/60Hz,
250V,
10A
EU
Plug: Demko (130778-01)
Cord: Demko (95-0272/95117)
Connector: Demko
(98-01458/124208)
H.R.SILVINE-CMC CO., LTD. CAT-209
H05VV-F 3G
EF-28
50/60Hz,
250V,
10A
Singapore
Plug: PSB (CPA JIR PLR 026158-00)
Cord: VDE (129752)
Connector: ASTA (14119)
HWAJIN KDK CO., LTD. KKP-4819KA
KKS-16K
KS KCCE-3
50/60Hz,
250V,
7A
Korea
Plug: KSC 3304 (8698)
Cord: KTL (SA04001-3004)
Connector: KSC 8305 (8697)
2

Introduction
Please Note!
This manual assumes use of microphone-level inputs and line-level output, the
most typical SmartMixer application. However, all inputs and the output may be
individually switched via the included SmartMixer Software to achieve any
combination of mic- and line-level input/output. Refer to Software Manual for
more information.
About the AT-MX381 SmartMixer
Audio-Technica’s AT-MX381 SmartMixer is a microprocessor-controlled, pro-
grammable, automatic-switching eight-channel audio mixer. It can be used
with low-impedance dynamic and condenser microphones (including wireless
microphone systems), as well as with line-level sources.
The AT-MX381 is designed to improve audio quality in broadcast, sound-rein-
forcement and recording applications. One of the ways it achieves this is by
keeping the number of open microphones to a minimum, thus reducing back-
ground noise, feedback and other distractions, while providing instant, com-
pletely transparent switching between channels.
Each of the AT-MX381 SmartMixer’s eight balanced inputs provides switchable
48-volt phantom power; attenuation is also selectable on each input to allow
use with line-level signals. The mixer’s main output is balanced and non-invert-
ing. In addition to a single main output, individual direct outputs are provided
for each input channel. All audio connections terminate in block screw con-
nectors.
Up to 16 AT-MX381 SmartMixers (a total of 128 channels) can be daisy-chained
via the included Link Cable, which carries control bus, audio, and configuration
data between mixers. Multiple mixers linked in this way will operate as if they
were a single mixer. Therefore, microphones activated on any mixer will cause
the appropriate switching functions to occur. Due to the link data protocol
(used for computer control and external RS232 control), AT-MX351 and AT-
MX341a SmartMixers cannot be linked to AT-MX381 SmartMixers.
The AT-MX381 includes two separate external control systems: Individual-
channel contact closures (via DB25 connector) and PC control (via RS232 con-
nector). The RS232 connector can also be used to connect an external control
system (Crestron® or AMX®) using “open disclosure communication proto-
col” to control the SmartMixer.
Overview of AT-MX381 Features
• Eight balanced inputs allow use with both mic and line-level signals. Each
input provides:
°48V phantom power (individually selectable)
°Individual gain and sound volume controls
°Gate attenuation adjustable (0 dB to full mute in steps of 12 dB)
°Low-cut filter (individually selectable via SmartMixer Software) to
minimize the pickup of undesirable noise
• NOMA (Number of Open Mics Attenuated) (selectable)—Automatic gain
adjustment as each microphone is activated
• Selectable manual mode overrides automatic functions
• Selectable hold time allows mics to stay on during brief pauses in conver-
sation
• Linking capability for 16 units (up to 128 channels)
• External control capability enables the SmartMixer to activate other
devices
• An RS232 data port provides a connection point for a PC computer running
the SmartMixer Software to configure key operating functions.
• Compatible with Crestron® or AMX® systems
• Output level meter
• Monitor headphone output with level control
• Basic functions are set on the main unit; detailed setting through
SmartMixer Software
• Mounts in a single 19" rack space; includes rack mount adapters
Priority Pre-select
To custom-tailor conferencing needs, the mode of each microphone channel
can be independently switched. The combination of switch settings results in
three different modes of priority selection/operation. (See page 6, “Priority
Microphones and the Lockout Bus.”)
Last Mic On
In any of the three modes of operation, the last microphone “on” will remain
“on” when talking ceases, to provide continuous room ambience. This feature
is cascaded throughout all linked mixers so that only one microphone in the
entire system will remain on.
Gate Attenuation
When a microphone is “off,” its input is only attenuated. This attenuation is
factory set at -36 dB. The amount of “off ” attenuation (gate attenuation) can
be adjusted via SmartMixer Software. (See page 6, “Adjusting Gate
Attenuation.”)
Manual (Non-automatic) Mode
If the automatic functions are not desired, the SmartMixer can be placed in
manual mode, bypassing the mixer’s automatic switching and attenuation
functions, causing the unit to behave like a conventional mixer. In manual
mode, the level of each input is controlled via its front panel gain and level
controls.
NOMA (Number of Open Microphones Attenuated)
In a multiple-microphone system, as more microphones are turned on
(opened), the increased system gain can be a potential source of feedback.
The NOMA feature helps control feedback by compensating for the increase
in system gain. A built-in algorithm in the AT-MX381 recognizes how many
microphones are “on” and automatically adjusts the system gain accordingly.
Because use of NOMA is not always appropriate or desired, the AT-MX381 is
shipped with the NOMA function disabled. Refer to Software Manual for
instructions on enabling NOMA.
External Control Connector (25 Pin D-Sub)
To increase the integration flexibility of the AT-MX381 with external control
and indicator devices, a rear panel connector (25-pin) is provided. Three func-
tions are available for each input channel via this connector:
1. “Force-On” – allows an external contact closure to force its
associated input to turn on.
2. “Force-Off – allows an external contact closure to force its
associated input to turn off.
3. “Control Voltage Out” – a voltage appears when the associated
input’s gate opens or turns “on”.
Note: External contact closures override PC control.
Refer to the section “External Logic Switching & Control Voltage” on page 7
for additional information.
RS232 Control Port
A rear panel RS232 port (9-pin) is provided to allow for the connection of a
computer running the SmartMixer Software application or external control
system (Crestron® or AMX®) using open disclosure communications proto-
col. Refer to Control Function Table on Page 5 for information on items con-
trolled by the computer.
3

AT-MX381
Front Panel
AT-MX381
Rear Panel
Figure 1 - AT-MX381 Front Panel - Control Layout (Page 9)
1. Input Trim Control – (Outer knob)
Adjusts the input signal sensitivity for the channel.
2. Input Level Control – (Inner knob)
Adjusts the channel’s level.
Priority Select – (Push inner knob)
Push the Input Level Control to set priority for the channel. When priority is
set, the associated priority LED illuminates in the Channel Status Display.
Push Input Level Control again to turn off priority. Refer to section on
Priority Microphones and the Lock Out Bus (Page 6) to learn more.
*Lock mode Select – (Push inner knob for over a second)
Push the Input Level Control (CH1) and Master Volume Control [5] at the
same time to select Lock mode (Key-Lock on) or Normal operation (Key-
Lock off). Manual/Auto Mode Indicator [7] blinks when Lock mode is select.
3. Gate Active/Overload LED indicator
LED lights green when the associated channel’s gate is open (“on”) and
red when the signal may potentially overload.
4. P48/ATT. Input attenuator – (Recessed button)
This recessed button is used to select between input attenuation options
and phantom power level for the associated input. Use a small tool to
press the button and cycle between selections in the following progression:
0 dB (MIC)/Phantom OFF →0 dB/(MIC)/Phantom ON →-35 dB (LINE)/Phantom OFF
The Channel Status Display LEDs illuminates according to selection.
5. Master Volume Control – (Inner knob)
Adjusts the mixer’s overall output. Turn clockwise to increase output.
Push to select Manual or Auto Mixer mode.
6. Threshold Level Control – (Outer knob)
Adjusts the threshold point at which the gates open and activate a channel.
When the outer knob is set at MIN, the threshold level is down and relatively
low levels of sound activate a channel; when set at MAX, the threshold
level is high. Turn clockwise to increase threshold; counterclockwise to
decrease threshold.
7. Manual/Auto Mode Indicator
This LED lights green when AT-MX381 is in automatic mode; it lights red
when the mixer is in manual mode; it blinks when the mixer is locked (Key-
Lock on).
8. Output Attenuator – (Recessed Button)
Switches the output attenuator on (-35 dB of attenuation) or off (0 dB of
attenuation). (Use a small tool to press the button and cycle between
selections.) ATT. LED illuminates in Output Status Display.
9. Output Status Display
LED level display indicates output level of mixer.
ATT. Lights green when the output attenuator is on (-35 dB of attenuation)
LEVEL: Indicates output level. This display can be set via SmartMixer
Software to indicate output level before or after the Master Volume
Control. (Default setting is “before” master control.)
10. Channel Status Display
LEDs indicate channel settings for each input.
a. ATT. – LED lights green when the attenuator is on (LINE level input).
4
Figure 2 - AT-MX381 Rear Panel (Page 9)
14. Power Switch
15. External Control Connector (25 pin D-Sub Female)
Provides connection points for controlling AT-MX381 from external
contact closures and control voltage output per channel. Refer to
“External Logic Connections” for more information on this connector.
16. Serial Data Connector (PC Control)
RS232 data port. Use with PC for configuring internal mixer settings or as
input point for CRESTRON®, AMX® or other control system using open
communications protocol.
17. Link In/Link Out connectors
Provides for daisy-chaining of multiple mixers when more than eight
microphones are used. (Use included link cable to connect to another
AT-MX381.)
18. Output Connector (4-pin block screw connector)
Pin-1: Hot, Pin-2: Cold, Pin-3: Ground, Pin-4: Line Out
Provides balanced main mixer output (selectable with or without 35 dB of
attenuation) along with second unbalanced output (line level) with no
attenuation available.
19. Input Con0nector (4-pin block screw connector)
Pin-1: Hot, Pin-2: Cold, Pin-3: Ground, Pin-4: Direct Out
Input connection for each channel. Also provides DIRECT OUT for given
channel.
b. P48 – LED lights green when channel phantom power is on.
c. PRIORITY – LED lights green when channel is set for priority mode.
(Note: When input attenuator is on (Line level input), the P48 phantom
power supply is disabled.)
11. Headphone Jack (1/4” stereo type)
Connect stereo headphones to monitor mixer’s output.
WARNING: do not connect MONO 1/4” plug, as it can damage the
mixer’s headphone amp.
12. Headphone Level Control
13. Power “on” indicator

Control
Function Table
Installation
and Setup
Many AT-MX381 functions can be configured and accessed over the RS232
data port by a PC running the SmartMixer Software (included) or by an exter-
nal control system (Crestron® or AMX®) using “Open Disclosure Protocol.”
This capability along with the contact closure inputs and control voltage out-
puts accessed through the External Control Connector provides for maximum
flexibility when interfacing the AT-MX381 to other equipment.
The table below lists the AT-MX381’s controllable functions and their factory
default settings.
* Can only be accessed via 25-Pin D-sub
External Control Connector on unit.
** Note: Force-ON/OFF contact closures
override PC control fuctions. Channels
forced ON or OFF using these control
points will NOT be reflected in the PC
control system.
Function Default setting From Unit
Function accessibility
From RS232
Data (PC)
Channel Trim Minimum NoYes
Channel Level Minimum NoYes
Input Attenuation
(No attenuation; no attenuation P48; attenuation) 0 dB YesYes
Phantom Power (Per Input) Off YesYes
Channel Priority Select (Per Input) Off YesYes
Threshold Level Minimum YesYes
Mode (Manual/Auto Mixer) Auto Mixer YesYes
Output Attenuation 0 dB (no attenuation) YesYes
PC Control Force – ON** Off YesNo
PC Control Force – OFF** Off YesNo
Force – ON Override (Per Input) Off NoYes*
Force – OFF Override (Per Input) Off NoYes*
Direct Output Select (Pre/Post Gate) Post Gate YesNo
NOMA Off YesNo
Gate Hold Time (Per Input) 1.0 Second YesNo
Gate Attenuation (Per Input) 36 dB YesNo
Low Cut Filter (Per Input) Off YesNo
“Last Mic On” On YesNo
Output Limiter (Overall) Off YesNo
Output Level Indicator (Pre/Post Master) Pre Master YesNo
Lock Mode (Control Lockout) Disabled YesYes
Refer to the section on Computer
Control for information on connecting a
PC computer, installing the SmartMixer
Software control software and using the
software.
Out of the box, the AT-MX381 comes configured for most common applica-
tions. Here are some basic SmartMixer setup tips to help quickly get up and
running: (Items in brackets [ ] refer to control locations on the diagram.) Note
an audio line level source may be substituted for any “microphone”.
AT-MX381 SmartMixer quick setup tips:
Figure 1 - AT-MX381 Front Panel - Control Layout (Page 9)
1. Turn the Master Volume control (inner knob) to the minimum position
(counterclockwise). [5]
2. Turn the Threshold control (outer knob) to the minimum position (counter-
clockwise). [6]
3. Turn all eight Input Trim and Input Level controls to their minimum position
(fully counterclockwise). [1,2]
4. Connect the power cord to the mixer and plug into an AC outlet. (The AT-
MX381 will automatically detect and select the proper AC voltage setting
based on line voltage connected.)
5. Turn Power switch “on.” The mixer will perform a self-test and flash each
input’s Gate LED. (Power switch is on rear of SmartMixer.)
Adjusts the mixer’s overall output. Turn clockwise to increase output.
Push to select Manual or Auto Mixer mode.
6. Connect a microphone to Input 1. Select the proper input attenuation and
phantom power with the P48/ATT button. (Use a small-tipped tool to push
the recessed button.) [4]
7. Turn the Input 1 Trim control to the “twelve o’clock” position. The channel
1 LED will light green if the microphone is operational and red if the trim
control is set too high.
8. Adjust the Input 1 Level control and observe the Output Status Level
Display for proper meter indication when speaking into microphone
(peaks at 0). [9]
9. Plug in up to seven other microphones and adjust the Attenuation, Trim
and Level controls for each microphone until proper meter indication is
obtained. Select NOMA, if desired.
10. Priority can be assigned to one or more microphones by pressing its Level
control; observe the priority indicators on the Channel Status Indicator
Display.[10] Any microphone(s) assigned in this manner cannot be locked
out by any other microphone.
11. “Manual” mode can be selected at any time by pressing the Master
Volume control and observing the Manual/Auto mode indicator. In this
mode, the unit will behave like a conventional mixer (all automatic func-
tions are bypassed except for limiting and NOMA if selected). [10]
12. Adjust the Master Volume control for desired output level. This control is
at the last stage in the mixer signal chain, and does not affect microphone
gain, threshold setting, meter indication, monitor or direct outputs. [5]
13. Adjust the Threshold control as desired. If signal does not open the gates,
reduce threshold level. If undesirable sounds open the gates, increase
threshold level. [6]
5

6
Priority Microphones and the Lockout Bus (Channels 1-8)
Once the Input Level controls have been properly adjusted, an audio signal
appearing in any channel causes the lockout control bus to activate. The prior-
ity settings associated with each input channel then determine whether or not
a particular mic is affected by lockouts caused by other mics.
When a channel’s Priority is OFF, other channels can lock out its mic.
When a channel’s Priority is set to ON, it will not allow lockout of its mic.
* Note that any mic that is described as “locked out” or “off “ is really just
being attenuated by between 6 dB and 96 dB from the level otherwise deter-
mined by its Level and Trim control setting, sensitivity and placement. See the
“Daisy-chaining Mixers” section on Page 7 for further details.
How Priority is assigned for the input channels determines the overall auto-
matic mixing operation. By incorporating the priority settings along with exter-
nal control and computer PC (RS232) Control, complex applications are easily
handled by the SmartMixer. The three most common “modes” of priority pre-
select automatic operation are:
Mode 1… None of the inputs have Priority selected.
In this mode, only one mic can be “on” at a time. The lockout bus shuts
down all other mics until the first speaker pauses. As soon as the con-
trolling microphone goes silent, the lockout bus goes inactive and any
other mic can come on. All switching takes place without any syllable-
grabbing delay, pops or clicks.
This mode is very useful when the gain setting of the overall sound sys-
tem must be close to the threshold of feedback, and additional micro-
phones coming on could throw the system into feedback. The
SmartMixer will not allow multiple microphones to be on at the same
time in this mode. The switching is so fast and silent that the meeting
can still be completely interactive.
Mode 2… One or more inputs have Priority selected
The selected priority microphone(s) can come on at any time and can
override any other mics (that are not priority mics). (Note that there may
be circumstances where more than one mic can be set to priority; the
priority speakers talk whenever desired, and override the non-priority
mics.)
Mode 3… All of the inputs have Priority selected.
The lockout bus will activate with any audio input, but no mic will be
locked out…because none are connected to the lockout bus.
Note: If multiple AT-MX381SmartMixers are used with AT8325/1.0 Link Cables,
Priority Pre-select switches on all channels in use will have the control effects
described above for the entire system.
NOMA
Number of Open Microphones Attenuated
In a multiple-microphone system, as more microphones are turned on
(opened), the increased system gain can be a potential source of feedback.
The NOMA system helps control feedback by compensating for the increase
in system gain. A built-in matrix in the AT-MX381 recognizes how many micro-
phones are “on” and automatically adjusts the system gain accordingly.
Because use of NOMA is not always appropriate or desired, the AT-MX381 is
shipped with the NOMA function factory set in the “off ” position. NOMA can
be enabled though the RS232 interface by using a PC running the SmartMixer
Software.
NOMA serves to maintain overall system gain by proportionately reducing the
mixer output level as the number of open microphones increases. (Typically,
attenuation is about 3 dB per additional open microphone.) In a sound rein-
forcement system, this can tend to preserve the feedback margin and system
stability. However, this action necessarily reduces the sound level of each
individual person speaking, which may not be desired. In the end, use of
NOMA often comes down to the preferences of the system’s designer and/or
operator. Generally speaking, use of NOMA is not desirable in applications
such as teleconferencing, recording or broadcasting.
Preamplifier Gain
The SmartMixer has a substantial gain range, allowing it to accept a wide vari-
ety of microphones and line level input sources. However, if in some instances
higher-output microphones are used for close talking, it may be necessary to
reduce the preamplifier gain. Turn the Input Trim control associated with each
input channel counterclockwise (CCW) to reduce the gain. Likewise, turning
the control clockwise (CW) will increase the gain for lower-output sources. In
addition for Line Level sources, the input can be attenuated by 35 dB by push-
ing the recessed “Input Attenuator Select” button twice; this will light the ATT.
LED for the selected channel. (Note, when attenuation is selected, phantom
power is automatically turned off.)
Phantom Power
Each of the SmartMixer’s inputs can supply +48V DC phantom power (default
off). To turn phantom power on or off for a given input, simply push the
recessed P48/ATT. button associated with each channel (using a small tool).
When phantom power is turned on for a given channel, the P48 LED associat-
ed with the channel illuminates in the Channel Status Display. Note that,
although they do not require phantom power for operation, most balanced-
output dynamic microphones can be used without disabling the SmartMixer’s
phantom power.
Output Limiter
The AT-MX381 includes a switchable output limiter circuit. When engaged, the
limiter helps prevent distortion caused by loud audio peaks. The limiter is fac-
tory configured for optimum operation (no user settings) and is turned ON or
OFF (default is OFF) from a PC running the SmartMixer Software.
Output Level
The SmartMixer’s output is factory set to no output attenuation (line level).
Should attenuated output be desired (mic level), simply push the recessed
ATT. button located next to the Master Level/Threshold control (using a small
tool). The ATT. LED will illuminate in the Output Display.
Output Level LED Meter
The Output Level LED meter is factory set to indicate audio level before the
Master Level control. This allows the meter to be used for setting up the
SmartMixer with the Master Level control turned down and no audio appear-
ing at the main output. If it is desired to have the meter affected by the master
volume control, it can be changed using a PC via the RS232 port. (Refer to
SmartMixer Software Master Control Section.)
Last Mic On
It is often desirable to have the most recently used microphone remain “on” to
provide continuous room ambiance. This feature is software selectable
(default – on) and is cascaded throughout all linked mixers so that only one
microphone in the entire system will remain on.
Adjusting Gate Attenuation (“OFF”)
When a microphone is “off,” its input is only attenuated. The attenuation level
(gate attenuation) is adjustable (0 dB to full mute) via the SmartMixer Software.
In instances when the number of microphones in use is high, it may be neces-
sary to increase the amount of gate attenuation (“OFF”) per microphone to
keep the total ambient noise level low. Each input channel can have its gate
attenuation set individually via a PC running the SmartMixer Software. The
gate attenuation can be set anywhere from 0 dB to -96 dB and full mute in 12
dB steps. (Default setting is –36 dB.) (Refer to SmartMixer Software Channel
Setting Section.)
Adjusting Gate Hold Time
Some applications may require that a microphone remain on for a longer peri-
od after a person stops speaking. If, for instance, the speaker pauses fre-
quently, it may be undesirable for the system to switch the mic off. Each chan-
nel’s Gate Hold Time can be adjusted in .5-second (half-second) steps from .5
seconds to 3 seconds. (The default is 1 second.) (Refer to SmartMixer
Software System Setting Section.)

7
Preamp Outputs
Each microphone channel has an independent unbalanced preamp output that
is separate from the main mixer output. This is the Direct Output pin on the
block screw connector for each input. This is helpful when it is necessary to
record the output of each individual channel, whether or not it is the active
mixer output (as is required, for example, in some courtroom proceedings).
These outputs can be configured before or after the channel’s gate (default is
before gate). (Refer to SmartMixer Software Channel Setting Section.)
External Logic Switching and Control Voltage
The AT-MX381 is provided with external logic switching and control voltage
connections for each of the input channels, allowing the unit to be interfaced
with a wide variety of control and monitoring systems. By creatively using the
external control connections, the flexibility of the AT-MX381 can be expanded
far beyond basic automatic mixing. The following logic functions are provided
for each input channel.
Force-on
When a contact closure is provided between the Ch * - Force On con-
nection and ground (* indicates the channel number), that input is
“forced on” and will override any priority settings (front panel or software).
Force-off
When a contact closure is provided between the Ch * - Force Off con-
nection and ground (* indicated the channel number), that input is
“forced off” overriding any priority settings (front panel or software).
Gate Status Voltage Out
When a microphone channel turns “on,” as indicated by its Gate LED on
the front panel, the channel’s associated Gate Status (control voltage
out) goes “high” (+4 VDC). This signal can be used to light indicator
LED’s or drive logic circuitry to, switch speaker zones on and off, select
video cameras, etc.
NOTE: The control voltage should not be connected directly to an inductive
load such as a relay coil, as damage to the mixer may result.
External Logic Connections
Connections for the external logic and control voltage appear on the rear
panel 25-Pin D-sub connector. It is designed to mate with a standard 25-Pin
Male D-sub connector (not provided). For connector pin-out assignments refer
to Table #1 below.
Note: External contact closures override PC control.
Using Force-on/Force-off
To activate force-on/force-off, install a clo-
sure between the appropriate pin and
Ground Reference on the External Control
connector on back of unit.
Note: Force-ON/OFF contact closures override PC control fuctions. Channels
forced ON or OFF using these control points will NOT be reflected in the PC
control system.
Using Control Voltage Out
When a microphone channel
turns “on,” as indicated by a
Selected Channel LED on the
front panel, the channel’s asso-
ciated Control Voltage Out goes
“high” (+4VDC). See chart pin
connection. This signal can be
used to light indicator lamps,
switch speakers zones on and
off, select video cameras, etc.
The control voltage should not
be connected directly to an
inductive load such as a relay coil, as damage to the mixer may result.
When more than eight microphones are needed, it is possible to daisy chain
multiple AT-MX381 SmartMixers together through the Link In/Out connectors
on their back panels (Fig. 2). Each AT-MX381 is supplied with a Link Cable that
carries control bus, audio, and configuration data between mixers. When
linked, all microphones in a multi-mixer system can be controlled by one
microphone connected to any mixer. Up to 16 AT-MX381 SmartMixers may be
daisy chained for a total of 128 input channels. However, due to the link data
protocol (used for the SmartMixer Software computer control and external
RS232 control), AT-MX351 and/or AT-MX341a SmartMixers cannot be linked to
an AT-MX381.
When running the provided link cables from one unit to another, connect the
cable from the LINK IN jack on Mixer #1 to the LINK OUT jack on Mixer #2, the
cable from the the LINK IN jack on Mixer #2 to the LINK OUT jack on Mixer #3,
etc. DO NOT connect a link cable from the last AT-MX381 back to the Master.
When linked, Mixer #1 becomes the Master; its output contains audio from all
mixers in the chain (Slaves). Each subsequent mixer in the chain will output its
eight inputs along with the inputs of those after it. The combined output is
then taken from the first mixer (Master) in the chain. Because lockout informa-
tion is passed between mixers through Link In/Out, the last-microphone-on
condition is not violated.
Example using three AT-MX381 SmartMixers:
Mixer #1 is the Master and receives all audio. Mixer #2 (Slave 1) receives
audio from Mixer #2 and Mixer #3 (Slave 2). Mixer #3 receives audio only from
its eight inputs. (Refer to Figure 3 on page 9)
Since the link cables pass control data along with audio, each mixer in the
chain is assigned an address upon power up. To ensure proper address
assignment, always power up Slave AT-MX381 units before applying power to
the Master. Alternatively, a power distribution scheme that applies power to
all connected devices at the same time may be used (i.e. a switched plug
strip).
Note that one or more mixers can be switched to “Manual” mode without
affecting the automatic operation of any other mixers in the chain.
NOMA information is passed between AT-MX381 mixers through Link In/Out. If
one or more of the linked AT-MX381 units has NOMA switched off, its micro-
phones will not be included in the NOMA calculation. Refer to NOMA section
for more information.
Pin # I/O
1Input Logic Function Ch. 1 Force ON
2Input Ch. 1 Force ON
3Output Ch. 1 Gate Status
Voltage OUt
4Input Ch. 2 Force ON
5Input Ch. 2 Force ON
6Output Ch. 2 Gate Status
Voltage OUt
7Input Ch. 3 Force ON
8Input Ch. 3 Force ON
9Output Ch. 3 Gate Status
Voltage OUt
10 Input Ch. 4 Force ON
11 Input Ch. 4 Force ON
12 Output Ch. 4 Gate Status
Voltage OUt
Pin # I/O
13 Input Logic Function Ch. 5 Force ON
14 Input Ch. 5 Force ON
15 Output Ch. 5 Gate Status
Voltage OUt
16 Input Ch. 6 Force ON
17 Input Ch. 6 Force ON
18 Output Ch. 6 Gate Status
Voltage OUt
19 Input Ch. 7 Force ON
20 Input Ch. 7 Force ON
21 Output Ch. 7 Gate Status
Voltage OUt
22 Input Ch. 8 Force ON
23 Input Ch. 8 Force ON
25 Ground (common)
24 Output Ch. 8 Gate Status
Voltage OUt
Table #1 DB-25 Connector Pin-outs
NOTE: This connector is NOT a computer data port. Connecting a computer or
other data device directly to it may cause damage to the device or the
SmartMixer.
IN
GND
OUT
LED
GND
Daisy-chaining
Mixers

8
The RS232 data port provides a place to connect a PC computer for system
configuration using the included SmartMixer Software. (Refer to the Software
Section for installing/using the software.) Alternatively, the data port may be
used to connect to an external control system such as Crestron® or AMX®
running “open disclosure communications protocol”. Refer to information from
control system manufacturer regarding using this feature.
In a system with multiple linked AT-MX381’s, connect the PC or control system
to the first (Master) unit in the chain. This will allow access to all of the linked
units for configuration and control programming.
RS232
Data Port
The AT-MX381 is designed to mount in a standard equipment rack occupying
a single rack space. For tabletop mounting, attach the included feet to the bot-
tom of the unit.
Rack
Mounting
For permanent installations where microphone selections, positions and
acoustic conditions are constant, it may be advantageous to lock out the front
panel knobs and functions to prevent unauthorized adjustments. To initiate
Lockout, activate the lock switch or activate the lock function via the
SmartMixer Software. (PC)
Control
Lockout
Specifications†
Input Impedance
Mic Level 6600 ohms
Line Level 8500 ohms
Output Impedance
Balanced
Line Level 300 ohms
Mic Level 350 ohms
Unbalanced 400 ohms
Direct Output 60 ohms
Maximum Input Level -50 dBu (gain at Max)
Maximum Output Level 22 dBm (THD+N at 1%)
Equivalent Input Noise Level -130 dBu *
Total Harmonic Distortion >0.3% (Channel gain at max)
Maximum Gain 69 dB
Frequency Response 20 to 20,000 Hz (±3 dB)
Microphone Phantom Power +48V DC
Control Voltage Out +4V DC
Maximum Monitor Output 50mW (@ 1% THD+N) with 16 ohms load
Power Supply 100 – 240V AC, 50/60 Hz, 20W
Dimensions 16.93” (430 mm) W x 9.05” (230 mm) D x
1.75” (44 mm) H
(not including feet, knobs and connectors)
Weight 3.4 kg (8 lb 6 oz)
†In the interest of standards development, A.T.U.S. offers full details on its test methods to other industry
professionals on request.
* Input terminated with 150 Ohm, A-Weighted using Audio-Precision System Two
*Specifications are subject to change without notice.
AMX® is registered trademarks of AMX Corporation.
Crestron® is registered trademarks of Crestron International.

⑭ ⑯ ⑱⑮ ⑲⑰
1 Pin 2 Pin 3 Pin 4 Pin
8 CHANNEL AUTOMATIC MIXER AT-MX381
POWER
MIN
MIN
MAX
MAX
LEVEL
MONITORGAINLEVEL
MIN
MIN
MAX
MAX
GA
GA
TE
GAINLEVEL
MIN
MIN
MAX
MAX
GA
GA
TE
GAINLEVEL
MIN
MIN
MAX
MAX
GA
GA
TE
GAINLEVEL
MIN
MIN
MAX
MAX
GA
GA
TE
GAINLEVEL
MIN
MIN
MAX
MAX
GA
GA
TE
GAINLEVEL
MIN
MIN
MAX
MAX
GA
GA
TE
GAINLEVEL LEVEL
MIN
MIN
MAX
MAX
GA
GA
TE
GAIN
MIN
MIN
MAX
MAX
GA
GA
TE
THRESHOLDLEVEL
MIN
MIN
MAX
MAX
AUTO
AUTO
ATT.
T.
P4
P4
8/
ATT.
T.
P4
P4
8/
ATT.
T.
P4
P4
8/
ATT.
T.
P4
P4
8/
ATT.
T.
P4
P4
8/
ATT.
T.
P4
P4
8/
ATT.
T.
P4
P4
8/
ATT.
T.
P4
P4
8/
ATT.
T.
ATT.
T.
+10
LEVEL
LEVEL
ATT.
T.
P4
P4
8 PRIORI
PRIORI
TY
+6
+3
0
-3
-6
-10
-20
20
CH
CH
8
CH
CH
7
CH
CH
6
CH
CH
5
CH
CH
4
CH
CH
3
CH
CH
2
CH
CH
1
OUT
OUT
PUT
PUT
CHANNEL
CHANNEL
STA
STA
TUS
US
Input
Input
1
1
Input
Input
2
2
Input
Input
3
3
Input
Input
4
4
Input
Input
5
5
Input
Input
6
6
Input
Input
7
7
Input
Input
8
8
Mas
Mas
ter
ter
①②
③④ ⑨ ⑩ ⑪
⑤⑥ ⑬⑫
⑦⑧
Figure 1 - AT-MX381 Front Panel - Control Layout
Figure 2 - AT-MX381 Rear Panel
FINAL OUTPUT
RS-232C
LINK IN
LINK OUT
LINK IN
LINK OUT
LINK IN
LINK OUT
PC
MASTER
SLAVE #1
SLAVE #2
SLAVE #n
Figure 3
9