A channel is a preset MotionBuilder facial expression that links the Actor Face with the Character Face.
While it is not absolutely necessary that you use these channels, they are the ones you will mostly likely need. You’ll want to have all of these channels mapped to shapes on your model. You can also consult the Character Face representation in the Preview pane, which demonstrates the expression you want each channel to create.
If Open is set to 100%, you get exactly what you modelled this shape into. MotionBuilder records the rate at which the change takes place when you move the slider. So this one channel can drive multiple shapes: including face shapes, tongue shapes, and teeth shapes. It’s driving three different parameters. You set those three parameters for one channel. You set these parameters to percentages that look normal for your model, not necessarily what we recommend in the manual.
There are two types of expression in Character Face settings: Generic and Custom expressions.