Automixer Technology¶

There are two general types of automixers built on different underlying technologies: Gating and Gain-sharing Automixers.

Gating automixers are more easily understood, so this article will cover their application first.

In a gating automixer, essentially each channel has a noise gate on it. The channel is either on, or off. The logic to decide whether a channel should be on, or off can be based on simply a fixed threshold, or it can be according to a complex equation which looks to priority levels, over-ride buttons, etc. This type of automixer also usually has a mechanism to lower the overall gain as more microphones are open. The terms number of open microphones (NOM) and NOM attenuation are often used to describe this factor. A weakness of this system is that since noise gates are used, unnatural "chattering" effects can occur. Another issue is that the gate threshold must somehow be established to operate throughout the performance. This can make set-up and calibration more difficult.

While a gating automixer is built around noise gates, a gain-sharing automixer is built around expanders. In this type of automixer, a channel is not just on, or off, but can be anywhere in between. The more that one channel dominates the rest, the more gain it gets in relation to the other channels. If two, or more channels are at equal volumes, they receive equal gain. If a channel is receiving almost no signal, it receives almost no gain. In this way, the total gain is shared between all channels with the loudest channels receiving the most gain. Since this method uses expanders, operation is usually very smooth and natural with no chattering gates. Also, this method doesn't require that a threshold be set unlike with gating automixers. A threshold is used by the expanders, but it is adaptively sensed using all of the existing microphones and doesn't require any user adjustment, or dedicated sense microphones. Also, NOM attenuation happens automatically since the total gain is shared between all channels. It should be noted that NOM is not a very useful concept with the gain-sharing type of automixers, since a channel is not just on, or off.