To illustrate the philosophy of the RM4200D system, we will use a common example: The configuration of a fader channel and the way an audio signal may typically take through the system. Please note that the following description gives only a very simplified overview. How things are done in detail is explained in the reference part of this manual.
Setting up a fader channel is done completely within the configuration software. A fader channel can use the following functions:
Input Routing. A fader channel always carries the signal of one audio input at the time. If a certain audio input port is assigned to one particular fader only, it is called a fixed fader channel. However, any fader channel can be configured to allow the user to select one of several input channels. To achieve this, a pool of inputs is defined in the configuration software. Thus, one ore more physical faders are assigned to this pool. Any fader belonging to the pool can now be used to access any input signal from the pool. These faders are called pool faders. To change the selected input for a fader, the user presses the Access button on the fader channel and rotates the Main Function Selector to pick the desired channel. Please note, that a channel from the pool can only be routed to one fader at the time – not to two faders simultaneously.
Input Processing. Every input channel can provide processing for its signal. Available processings are equalizer, limiter, compressor, expander, noise gate, subsonic filter and others. Up to four equalizers can be cascaded if desired. All input processing is configured from the software, but all parameters for the processing can be changed using the controls on the mixer console. Please note, that the parameters for the processing stay with each input channel, no matter if it is currently linked to a fader channel or not. The total amount of processing available to all channels depends on the available DSP resources. However, in a typical RM4200D application, these resources are plenty.
Bus Assignment for summing, monitor and Aux buses. Any channel can be configured to have its signal routed to one or more different buses for summing, monitoring and Aux bus processing.
Clean feed (mix-minus) and talkback setup. Any input channel can be defined to provide a clean feed signal (sometimes also called mix-minus signal). This signal is available on the TDM bus an can be used for custom talk-back applications.
Logic Function definition. The configuration software allows to define logic functions for any input channel. A typical example would be to switch on an On Air lamp when a microphone fader is opened. However, much more sophisticated function are possible using the RM4200D Control Engine. Using GPOs, a fader start can trigger events to external systems – like the remote start of a DAT machine. If desired, a LED in a push button of a control module can be defined to signal any condition from the Control Engine, not just “Fader On” and “PFL Active” for the given fader channel.
Now that the fader channel is configured properly, its signal is available on the TDM bus. The Control Engine affects the Audio Engine using Output Functions. This is a simple, yet powerful concept, that allows any logic condition to affect any desired audio signal in a predetermined way. It is explained in detail in the reference volume of this manual.
Finally, the audio signals on the TDM bus must be routed to physical output ports. Any audio signal on the TDM bus can be routed to one (and only one) output port. If desired, the signal can be processed once again before leaving the RM4200D system. This is called Fixed Processing. Typically this includes compressing, limiting and other sound improvement of the On Air signal.