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Inhibiting Gating for Unwanted Sounds
MaxBus attempts to activate only one microphone per sound
source. Muting a microphone channel prevents its audio from
appearing at the mixer’s output. However, the muted micro-
phone still communicates with other mic channels via Max-
Bus.
A sound source picked up by a muted microphone will not
activate other microphones.
Sound sources that may cause unwanted microphone chan-
nel activation include:
• Heating, ventilation, or air conditioning systems
• A noisy fax machine or printer
• A squeaky door
• A paging system loudspeaker
• An audio teleconferencing return signal loudspeaker
The SCM410 can prevent these and similar sounds from acti-
vating microphones as follows:
1.Place one microphone near the unwanted sound source.
Connect that microphone’s signal to a channel input,
—or
—
connect the unwanted sound source directly into a channel
input.
2.Mute that channel using the logic terminal (see Figure 24).
To perform this modification internally on the mixer, refer to
the
Shorting Mute In to Logic Ground Internally
paragraph in
the
Internal Modifications
section.
3.Adjust the channel gain control just past the level where un-
wanted sounds do not activate other microphones in the
system. If the channel gain is set too high, the other micro-
phones may not be activated by the
desired
sounds. If set
too low, unwanted sounds will continue to activate other mi-
crophones.
M1
LOGIC
GROUND
INHIBITING GATING FOR UNWANTED SOUNDS
FIGURE 24
Loudspeaker Muting
Some applications require a loudspeaker to be placed near
each talker to provide audio reinforcement, or to permit tele-
phone conversation or conference monitoring. Each loud-
speaker can cause feedback unless it is automatically switched
off when the talker near it speaks. To provide this function, con-
nect the GATE OUT terminal of each channel to a separate
loudspeaker muting relay (See Figure 25). Recommended re-
lays are Radio Shack 275–248, Omron G2R-14-DC12 (Digi-
Key number Z745-ND), Potter & Brumfield R10-E1Y2-V185
(Newark number 45F106), or equivalent.
NOTE
:
A diode across each relay coil is required to suppress
inductive voltage spikes which may damage the SCM410.
An existing sound system using 24-volt relays can be used
with the SCM410 without modification if the relay coil current
draw is under 500 mA.
+
–
12 V
POWER
SUPPLY
G3G1
DD
FROM
POWER AMP
D = 1N4148
LOGIC
GROUND
LOUDSPEAKER MUTING
FIGURE 25
“Filibuster” Mode
Normally, when several people talk, each microphone gates
on so that no speech is missed. In “filibuster” mode, a micro-
phone remains gated on until the talker pauses long enough
for that microphone to gate off. No other microphone can gate
on until that microphone gates off. This prevents talkers from
being interrupted.
To establish filibuster mode, refer to Figure 26 and proceed as
follows:
1.Perform the
Mute to Inhibit
modification as presented in the
Internal Modifications
section.
2.Connect all the MUTE IN pins together on the modified
channel.
3.Connect all the GATE OUT pins together on the modified
channels.
4.Connect the GATE OUT pin of one modified channel to the
MUTE IN pin of another modified channel .
5. Turn the Last Mic Lock-On switch to OFF.
NOTE: To prevent high-frequency oscillation, do not wire a
GATE OUT pin to a MUTE IN pin on the same channel unless
the
Mute to Inhibit
modification has been made.
G1
M1
G3
M3M2
LOGIC
GROUND
G2
“FILIBUSTER” MODE
FIGURE 26