User's Manual

12
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 microphone still communicates with
other mic channels via MaxBus. A sound source picked up by a muted mi-
crophone will not activate other microphones.
Sound sources that may cause unwanted microphone channel activa-
tion 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 activating
microphones as follows:
1. Place one microphone near the unwanted sound source. Con-
nect 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 11). 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
unwanted 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 micro-
phones.
LOUDSPEAKER MUTING
Some applications require a loudspeaker to be placed near each talker
to provide audio reinforcement, or to permit telephone conversation or
conference monitoring. Each loudspeaker can cause feedback unless it
is automatically switched off when the talker near it speaks. To provide
this function, connect the GATE OUT terminal of each channel to a sep-
arate loudspeaker muting relay (See Figure 12). Recommended relays
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.
“FILIBUSTER” MODE
Normally, when several people talk, each microphone gates on so that
no speech is missed. In “filibuster” mode, a microphone 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 pre-
vents talkers from being interrupted.
To establish filibuster mode, refer to Figure 13 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 channels.
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.
M1
INHIBITING GATING FOR UNWANTED SOUNDS
FIGURE 11
LOGIC
GROUND
+
–
G3G1
DD
D = 1N4148
LOUDSPEAKER MUTING
FIGURE 12
LOGIC
GROUND
12 V POWER
SUPPLY
G1
M1
G3
M3M2
G2
“FILIBUSTER” MODE
FIGURE 13
LOGIC
GROUND