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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
An existing sound system using
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, |
| 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 |
D | D |
G1
D = 1N4148
+
12 V POWER
SUPPLY
–
LOGIC
GROUND
G3
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. |
LOGIC
GROUND
M1
INHIBITING GATING FOR UNWANTED SOUNDS
FIGURE 11
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
NOTE: A diode across each relay coil is required to suppress inductive voltage spikes which may damage the SCM410.
LOUDSPEAKER MUTING
FIGURE 12
“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
NOTE: To prevent
| LOGIC |
G1 G2 G3 | GROUND |
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| M2 | M3 | ||
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“FILIBUSTER” MODE
FIGURE 13
12