In a networked audio system where multiple mixers are sharing the same stage box inputs, gain staging can become an issue. When the master mixer changes the analog gain of a mic preamp to optimize its internal gain staging, the signal level to every mixer on the network sharing that input changes as well.
There are two types of gain compensation that can be used to mitigate potential gain sharing issues: console gain compensation and local gain compensation (also known as constant gain).
With a console gain compensation scheme, one console is designated as the master control of the stage box inputs and the other is designated as the slave. The master console remotely controls the level of the stage box mic preamp over the audio network. When the stage box receives the gain change command from the master mixer, it makes the change, then sends a message to the slave mixer to compensate for the gain change using the slave mixer’s digital gain.
While this works for smaller systems, when more than two digital mixers are sharing a networked stage box, this scheme is no longer practical.
Local gain compensation, like that employed by PreSonus NSB-series stage boxes, can be used only if the stage box provides a dedicated DSP to compensate for the analog gain in the digital domain before sending the audio data out to the network. In this way, while a single master mixer is in control of the analog gain, ensuring that the signal is optimized before it reached the analog-to-digital converters, any mixer on the network can gain stage its sources locally for optimal performance. This makes this method of gain compensation much more practical for larger networked systems.
In a StudioLive Series III AVB network where multiple StudioLive Series III digital mixers are sharing the inputs from a single NSB stage box, once the preamp level is set by the master mixer, every other mixer on the network has the option of listening to the same stream or the gain compensated stream. Routing the AVB stream that isn’t gain compensated, means that any mixer listening to that stream will have no control over the level. While this may be fine in some situations, this could create gain staging issues in others.
Using the Gain Compensated (GC) stream on an NSB-series stage box allows each mixer on the network to retain independent gain control without potentially harming the Front-of-House mix. NSB stage boxes have an onboard DSP that adjusts the level of the gain compensated streams relative to gain set on the master mixer. In this way, every mixer on the network has a working gain range of +/- 20 dB, even if they are not the set as the master preamp controller for the stage box.
Once Gain Compensation is engaged, the Master mixer can adjust the gain of each NSB preamp +/- 15 dB before the change will be heard locally on any mixer receiving the Gain Compensated stream. When using a StudioLive Series III console as the master preamp controller for your NSB-series stage box, select the non-Gain Compensated streams for your inputs. Once you have optimized the analog input gain for your NSB-series stage box from the master mixer, enable Gain Compensation to provide every mixer listening to the gain compensated stream with local digital gain.