Video: Add a Matrix Mixer

Steps

In the Outputs window, open the Audio Mixer section, click the plus button, and choose Matrix.

Set its name, then its input and output counts. They do not have to match — that mismatch is the whole point of a matrix mixer.

Under Volume, you can set the level of each channel.

Expand Matrix and decide how each input channel feeds each output channel. This grid is the primary feature: You either choose a Preset or adjust the channels freely: a stereo pair spread across eight speakers, sixteen channels folded down to two, or one input muted without touching the rest.

Now open Audio Routing and connect the mixer to an audio output. A matrix mixer is free-standing — it reaches nothing until you do this.

Finally, in the Sequencer, set an audio channel's Destination to this mixer. Hovering it says "Assign to Matrix mixer", which is how you tell it apart from an output's own mixer.

If you now play this Sequence, the Audio will go to the Matrix mixer, which applies the changes you have selected and then forwards the Signal to the output selected in the Audio Routing. In our Case mixing a 5.1 Audio signal onto just 2 Speakers.