AGC and Automixing
It is often desirable to place dynamic processors such as Compressors and Automatic Gain Control (AGC) ahead of the Automixer DSP module however; this presents a small technical issue. Automixers determine which channels are active by discriminating between the differences in each channel’s signal level. Compressors or AGCs effectively minimize the differences between each channel’s signal level. This tech tip illustrates the recommended use of dynamic processing after an Automixer module.

Wiring and Module Layout
This example requires a single AGC module attached to the Mix out of the Automixer. The AGC Ctrl (control) output wires to the VCA Control input. (The VCA module is located in the Mixer and Matrixes section of the SymNet Designer toolkit). The VCA audio inputs are connected to the channel outputs of the Automixer. The VCA audio output is wired to a Matrix module to create mix-minus feeds for zones. Prior to the AGC is an Expander/Gate module that is used to remove the noise floor of the channel outputs as necessary.

Example 1 Image

VCA Max Gain Compensation
There is one more consideration; the VCA has a Max Gain parameter. Different dynamic processors send out different control signal levels so the Max Gain parameter is used to compensate for any differences. When using the AGC module in this fashion, the Max Gain needs to be at +36 dB.

Example 2 Image

More information on this subject is located in the SymNet help file. Within the Dynamics section, there is a heading titled “Creating Multi-channel Dynamics Modules” which discusses the VCA output settings for various Dynamic processors.

The intent of this design is to flatten out the mics so that soft and loud voices come out the speakers at the same volume. Many will argue that dynamics should be wired prior to the Automixer. However, this design serves to conserve DSP resources as well as allow the Automixer to do its job as designed. Give it try; you may be surprised with the results.