Inhibiting Gating for Unwanted Sounds

As described in the Operating Principles section, MaxBus attempts to acti- vate only one microphone per sound source. Muting a microphone channel prevents its audio from appearing at the mixer's output. However, the mut- ed microphone still communicates with other mic channels via MaxBus. A sound source picked up by a muted microphone will not activate other mi- crophones.

Sound sources that may cause unwanted microphone channel activation include:

•A noisy fax machine or printer

•A squeaky door

•A paging system loudspeaker

•An audio teleconferencing return signal loudspeaker

The SCM810 can prevent these and similar sounds from activating micro- phones by taking the following steps.

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 Mic/Line channel input.

2.Mute that channel using the logic terminal (see Figure 16-Channel 1 is muted).

3.Adjust that channel's gain control just to the level where other micro- phones in the system do not activate for the unwanted sound. If the channel gain is set too high, other system microphones will be difficult to activate for desired sounds. If set too low, unwanted sounds will continue to activate other microphones.

LOGIC

GROUND

INHIBITING GATING UNWANTED SOUNDS

FIGURE 16

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 separate loudspeaker muting relay as shown in Figure 17 (Channels 1, 3 and 5 shown modified). Recommended relays are Omron G6B-1174P-US-DC12, Potter & Brumfield R10-E1Y2-V185, or equivalent (available through Digi-Key and Newark Electronics).

NOTE: A diode across each relay coil is required to suppress inductive volt- age spikes which may damage the SCM810.

An existing sound system using 24-volt relays can be used with the SCM810 without modification if the relay coil current draw is under 500 mA.

12 V

POWER SUPPLY

–

LOGIC

GROUND

G1 G3G5

D = 1N4148

FROM

POWER

AMP

LOUDSPEAKER MUTING

FIGURE 17

“Filibuster” Mode

In normal operation, when several people talk, each microphone gates on so that no speech is missed. In “filibuster” action, a microphone that is gat- ed on prevents other microphones from gating on. Once a microphone has gated on, other microphones cannot gate on until the talker has paused long enough for that microphone to gate off. Thus the person talking has the floor and cannot be interrupted.

To establish this function, first perform the internal Mute to “Inhibit” modifi- cation (see Internal Modifications). Then connect all the MUTE IN pins of the modified channels together, all the GATE OUT pins of the modified channels together, and the GATE OUT pin of one modified channel to the MUTE IN pin of another modified channel (see Figure 18-Channels 1, 2 and 3 modified). Turn the Last Mic Lock-On switch (SW702, position 2) to off.

NOTE: To prevent high-frequency oscillation, do not wire a channel's GATE OUT pin to its own MUTE IN pin unless the Mute to “Inhibit” change has been made.

LOGIC

G3GROUND

JUMPER

G1 M1 M3

G2 M2

“FILIBUSTER” MODE

FIGURE 18

Inhibit Function

See Internal Modifications