Schematic Legend
Gated Automatic Mixer
Purpose
The Gated Automatic Mixer is a combination of a mixer, gates and priority logic. It is designed for panels, board-rooms and other applications where there are numerous microphones though generally only a few are in use at any time. Gated The Automatic Mixer improves system performance in these situations with the following features:
Gates out background noise entering the system from inactive microphones.
Allows a higher gain before feedback by controlling and compensating for the number of open mics (NOM) in the system.
Enforces pecking order through a priority logic mechanism.
Inputs
There is a single input for each source to be automatically mixed.
Outputs
There is a direct output for each input to the mixer. The gated version of each input is available at these outputs. The next output, labeled "M", is the mixed sum of the gated inputs, attenuated by the NOM compensation factor.
Controls
Causes the effective Input Threshold Level settings to be nudged upwards as the overall volume input to the mixer raises. This prevents gates from opening unintentionally as the level of background noise received by the mixer increases.
Specifies the attenuation provided by the gate when in its closed state.
Determines how long the gate will remain open after the input signal falls below the Threshold Level
Inverts the polarity of the channel input.
Adjusts the level setting of the channel input.
It is possible to create an overload condition at the input of the mixer if this control is set above +0dB. Such an overload will be indicated by the channel's Input Overload indicator.
Input Mode (Filibuster/Manual/Auto/Priority)
Sets the conditions under which the channel will open.
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Filibuster |
The channel opens when the input signal exceeds the Input Threshold setting for the channel only if no other channel (regardless of mode) is already open. |
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Manual |
The channel is always open. When a channel is in Manual mode, the Open Indicator will remain lit. |
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Auto |
The channel opens when the input signal level exceeds the Input Threshold setting for the channel. |
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Priority |
The channel opens when the input signal level exceeds the Input Threshold setting and no channel in Priority mode with higher Priority Level setting is also open. |
Mutes the associated channel input.
Indicates the channel's gate is open. The gate opens when the input level exceeds the Input Threshold setting or if the channel is in Manual Input Mode. A gate may be closed or prevented from opening by the priority logic.
Indicates clipping on an input strip. Clipping is possible if the Input Level control is set above +0dB.
When the channel is in Priority Input Mode, this assigns a relative priority to the channel. This control has no effect when the channel is in Manual or Automatic modes.
When this channel opens, it will close any other channels in Priority Mode with a lower Priority Level setting.
Closes all other inputs which are not also Soloed. If any channels Solo button is engaged, only channels with solo engaged will be allowed to open. Solo overrides the Priority logic.
Specifies the input signal peak level above which the gate will open.
Limits the amount of NOM attenuation that can be applied to the output signal.
Indicates the attenuation currently applied at the output due to the current Number of Open Microphones and the current NOM Mode and NOM Attenuation Setup settings.
Specifies the rate at which attenuation is introduced at the mixer output based on the Number of Open Mics.
Indicates the number of microphone channels currently open.
Selects the nature of attenuation introduced as more mixer channels open. This feature helps prevent feedback in a system as well as keeps the overall sound level reasonable when several participants speak simultaneously.
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Exponential |
The output is attenuated by the amount specified by the NOM Attenuation Setup control each time the Number of Open Mics doubles. The output attenuation is adjusted in fractional Attenuation Steps as single channels open and close. The exponential response produces an optimally high gain before feedback for all possible open mic counts. |
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Linear |
The output is attenuated by the amount specified by the NOM Attenuation Step control for each open channel beyond the first. |
Determines how fast the NOM attenuation is applied at the output in response to a change in the Number of Open Microphones.
Last Mic On Switch
This switch holds the last microphone on, even if the signal level falls below the threshold point. It will remain on until another inputs signal level is higher than the threshold point, at which time, that microphone will stay on until the next microphones signal level is higher than the threshold point, etc.
Controls the output level from the mixer by reducing all contributions to the mix bus.
Indicates an overload on the mix bus.
Correcting a mix bus overload may be require reducing the Output Level and/or, despite what may be indicated in the slightly simplified Schematic, Input Levels for the open channels (and/or Gate Depth if no channels are open).
Schematic for a 2 input Automatic Mixer.