Gain-sharing Auto Mixer

Functionality

The Gain-Sharing Auto Mixer block automates the mix of multiple microphone input signals into a single output channel. The block sums all of the inputs, measures the level of that sum, and attenuates all inputs by the difference between their level and the level of the sum. The attenuated input signals are mixed together and sent to the output level control and meter. This simple algorithm amounts to automatically riding the channel faders on a mixer, turning up microphones in use, and pulling down faders for unused microphones to avoid feedback. The gain-sharing algorithm results in the same 3 dB attenuation per doubling of open microphones that you may be familiar with from working with gated automixers. However, gain-sharing goes further by maintaining a constant level of background noise reinforcement (without requiring the last mic on feature of gated automixers), attenuating two open mics with coherent input signals by 6 dB per mic (avoiding the 3 dB bump that gated mixers give to a talker who is equidistant from two microphones), eliminating gate thresholds that may trip erroneously due to background noise (unintentionally gating on all microphones), and eliminating gate timing (that could clip the first syllable off of a new talker’s speech). In general, gain-sharing mixers are easier to configure and operate than gated automixers, while sounding better too.

The Gain-sharing Auto Mixer also has a priority level setting. Any microphone input that has priority enabled lies to the gain-sharing algorithm, saying that it’s X dB hotter than it actually is (where X is the priority level). Effectively, this forces non-priority inputs to duck by the priority level whenever one or more people talk into one or more priority inputs.

How to Use

Use the Gain-Sharing Auto Mixer block to automatically mix multiple microphone input signals into a single output channel.

Adding the Block to Your System

Click the Processing tab to open the Processing Workspace.
In the palette area, click the DSP tab.
Expand the Mixers category of blocks.
Click and drag the Gain-sharing Auto Mixer block into your Processing Map.
Wire it into your system in the appropriate location. If you need additional inputs, simply wire to the <Add> node or click the <Add> text.
(Optional) Customize the names of the block and/or the input and output channels by clicking their current name and then typing the custom name in the text box that appears. Click the X to save the name.

Configuring the Block

Open the Gain-sharing Auto Mixer block's properties by double-clicking the block or hovering and clicking the properties icon that appears in the upper right of the block's title bar. The properties dialog box displays the input and output channels, displaying up to four input channels at a time. Use the scroll bar (located beneath the inputs) to bring other inputs into view. Each input channel includes both a Signal presence indicator and a Mute control that can mute the input so that it is silenced in all outputs.
note: These signal indicators are actually meters, therefore they are subject to the same 16 active meter limit as all other meters.

From this dialog box, you can do the following:

Enable inputs by ensuring that the channel is unmuted.
Decide if you want to give any inputs priority. If so, select their Priority checkbox and set the Priority Level to taste.
Control the mix volume. The output level controls the volume of the entire mix. To mute the mix output without changing the output level control, select the output's Mute checkbox.
Provide end user control over input mute, input priority, or output level by linking those controls to the relative controls on one or more DRs. For example, if the automixer is mixing a city council chamber, link to the output level to give the president control over the output volume. Link a DR or momentary switch to the president’s priority checkbox (with a priority level of 6 dB) to give the president a soft-override button, or link that override button to all the other council member’s input mutes to really let 'em know who’s boss.

User Interface Elements

Gain-sharing Auto Mixer Block

UI Element	Purpose
Input nodes	Connection points for wiring input to the Gain-sharing Auto Mixer block
Output node	Connection point for wiring the Gain-sharing Auto Mixer input to a specific output
<Add> nodes	Click to add another Input node, or wire to the <Add> node to automatically create a new channel.
Cascade In drop location	Drop location for cascading in an AM2, causing the AM2 to participate in the block's gain-sharing algorithm. note: After dropping an AM2 on this location, another drop location displays. You can drop up to 36 AM2s on this block.

Gain-sharing Auto Mixer Block Properties

(Hover over the thumbnail below to view the properties dialog box.)


UI Element	Purpose
Input Priority (Manual and Linkable Control)	Select to give an input priority. Provide end users with control over toggling the priority of an input by linking this Toggle Control to the Toggle Control of a DR2, DR3, or Logic In.
Priority Level	Set the additional dB value that the priority input(s) add to their actual signal level.
Input Mute (Manual and Linkable Control)	Mute this input. Provide end users with mute control by linking this Toggle Control to the Toggle Control of a DR2, DR3, or Logic In.
Input Signal	Lights when a signal is detected on this input, turns red if signal overload occurs.
Output Level (Manual and Linkable Control)	Control the volume of the entire mix. Provide end users with control over the output volume by linking this Level Control to the Level Control of a DR1 or DR3. Change the range by clicking the Minimum or Maximum value (below the slider) and then typing new values in the edit box that appears.
Output Mute (Manual and Linkable Control)	Mute the mix output without changing the output level control. Provide end users with output mute control by linking this Toggle Control to the Toggle Control of a DR2, DR3, or Logic In.
Output Off @ Min Checkbox	When checked, causes the audio to mute completely when dialed to the low end of its range.
Overall Mute Checkbox	Mute all outputs from the block. Manual control only.