Each input channel of the SCM410 or SCM810 has three Logic terminals:
Therefore, the SCM410, with four inputs, has 12 Logic terminals, plus a LOGIC GROUND terminal, for a total of 13. The SCM810, with eight inputs, has 24 Logic terminals, plus a LOGIC GROUND terminal, for a total of 25. These Logic terminals are on a multi-pin connector, located on the left side of the SCM mixer rear panel.
The LOGIC GROUND terminal never changes from its level of 0 volts.
First Logic Function – MUTE IN
When the MUTE IN terminal is connected to the LOGIC GROUND terminal, the associated input is muted. This connection can be accomplished using a switch, a relay, or an external control system.
How can MUTE IN be employed? Imagine a city council system with 16 microphone positions. Each position could have a switch so that the council member could mute her microphone for privacy. The mayor could be given a switch that mutes all the microphones in the chamber. There could be a main control console where the council secretary could mute and unmute microphones as required.
Second Logic Function – OVERRIDE IN
When the OVERRIDE IN terminal is connected to the LOGIC GROUND terminal, the associated input is activated, even if no one is speaking into the microphone. This connection can be accomplished using a switch, a relay, or an external control system.
How can OVERRIDE IN be employed? Imagine the same city council system. There could be a need to have a mixer input activated at all times, overriding the voice activation. This input might be used for audio from a DVD player or computer. Just remember that OVERRIDE IN is the opposite of MUTE IN.
Third Logic Function – GATE OUT
When the input channel is not activated (the talker is silent), the GATE OUT terminal has a voltage of +5 Vdc. When the input channel is activated (talker is speaking), the GATE OUT terminal changes to a voltage of 0 Vdc. Thus, the GATE OUT terminal will indicate if a mixer input channel is activated or not.
How can GATE OUT be employed in the same city council system? The GATE OUT could be used to trigger a video camera to view the person speaking. GATE OUT could be used to activate a light near the talker to indicate that the microphone is “live.” GATE OUT could be used to activate an external circuit that shuts off the loudspeaker nearest the microphone to control feedback. GATE OUT could also control the MUTE IN or the OVERRIDE IN associated with another input…think about that.
Again, there is a common element to all Logic functions discussed: a Logic terminal only has two states: +5 Volts or 0 Volts. As with the MX microphones and the SLX4L receiver, the Logic functions are elementary:
Mixer input- Muted or Not Muted (MUTE IN)
Mixer Input – Forced On or Not Forced On (OVERRIDE IN)
Mixer input – Activated or Not Activated (GATE OUT)
The User Guide for the SCM410, and for the SCM810, has a section that illustrates methods for using the Logic functions, including useful external Logic circuits.
Epilogue: Do not be concerned if the implementation of the Logic functions remains a bit fuzzy; Applications Engineering can help with those details. Just be cognizant of the Logic functions provided in the MX microphone line, the SLX4L receiver, and the SCM mixer line.
Related links on this topic:
Arcana – mysterious or specialized knowledge. Shure Applications Engineering is full of it.
One unique Logic function of the SCM810 is called Filibuster mode. When implemented, the first microphone that is voice activated will block out all other microphones. In Chicago, this mode is satirically referred to as “The Mayor Daley Option.”