CRR – Inputs, Outputs, and Routing

The Conference Room Router receives all the input signals for a single teleconference room and mixes them to produce all the required output signals for that room.

Mic Mix and Direct Mics
The Mic Mix input will always be present on any CRR and is labeled as “Post-AEC”. The Direct Mic inputs are disabled by default and may be enabled as needed. These are labeled as “Pre-AEC”. These two distinct types of signals are used for different purposes, come from different sources, and are routed differently inside the CRR.

Both of these types of signals are routed through an Automatic Microphone Mixer prior to the CRR, but the Post-AEC signal also passes through the Acoustic Echo Cancellation block. Pre-AEC microphone signals are used for local speaker outputs because they have a much lower latency than Post-AEC signals. The Pre-AEC microphone signals do not benefit from the echo cancellation of the AEC, but that’s not required for local speakers.

For example, Far End outputs are used for things like telephone and video codec connections. In these cases, a pre-AEC microphone signal will cause the Far End to hear echo, so the post-AEC microphone signal is always used.

All of the audio routing inside the CRR is handled automatically except speaker output routing. In every system, the Far End outputs require Post-AEC microphone signals to avoid hearing an echo in the far end, so the CRR will always use the Post-AEC microphone signals for far-end outputs. Aux outputs are designed to provide a full mix of the room for purposes such as recording and assisted listening systems, so these outputs require post-AEC microphone signals to avoid hearing the far-end microphones both directly and through the local microphones. The CRR will always use Post-AEC microphone signals for aux outputs.

For local speaker outputs, the latency of Post-AEC microphone signals can be excessive, so Pre-AEC microphone signals are used. While Far End and Aux outputs are routed automatically by the CRR, the routing requirements for microphones to the local speakers will be different for every room. There’s no way to predict these requirements, so the CRR creates the appropriate audio routing to allow only the Pre-AEC microphone signals to be sent to the local speakers, but the crosspoints are turned off by default and need to be configured to match the requirements of each room. If a system has no local voice-lift, the Direct Mic inputs can be left disabled as they will not be needed.

The Program input is used for signals such as computer audio, DVD players, and other local sources. If a system has multiple program sources, the sources are routed through a source selector or a mixer prior to entering the CRR. The Program input has relatively simple routing rules inside the CRR because it is available to every output. Aux outputs and Far End outputs automatically receive the Program input signal and local speaker outputs may receive the Program input signal. The crosspoint to route the Program input signal to the local, front speakers is on by default to simplify quick setup and testing of the system, but it may be turned off if needed and routed to different speaker outputs.

Far End
Far End signals have the most complex routing within the CRR because each Far End input needs to be routed to every output except its own output. If a Far End input is routed to its own output, the far-end will hear an echo of their own audio being sent back to them. This routing is handled automatically by the CRR to ensure that each of the far-end connections can hear all other far-end connections without hearing their own audio echoed back.

Far End signals are automatically routed to all Aux outputs to maintain the full room mix at those outputs.

Routing requirements for local speakers are impossible to predict, but each local speaker output needs to have the far-end signals available. The CRR provides crosspoints in the Speaker Matrix to allow the far-end signals to be routed to any of the local speaker outputs. The crosspoints for the Far End inputs to the local overhead speakers are enabled by default to facilitate system testing, but can be changed as needed in the speaker matrix control panel.

AEC Reference

The final output from the CRR is the AEC reference output. The rules for AEC reference input assignment are simple: the AEC reference MUST receive every Far End input signal. In some cases, the AEC reference MAY receive the Program input signal, but the AEC reference must NEVER receive its own microphone signals. In the CRR, all Far End inputs are always routed to the AEC reference outputs. Routing the Program input to the AEC reference is not required, but it does provide clearer audio for the Program sources, so the Program input in the CRR is also routed to the AEC reference. Microphone signals are not routed to the AEC reference because that would cause the AEC reference to attempt to remove the microphone signal from itself.