Connect a PassThrough unit to the input ports of the voices
so that they can be controlled together using a single port.
Note that this will prevent their individual use.
So the "Frequency" and "Amplitude" ports are excluded.
Note that this method is a bit funky and is likely to change.
public void exportNamedInputPort(java.lang.String portName)
Create a UnitInputPort for the circuit that is connected to the
named port on each voice through a PassThrough unit.
This allows you to control all of the voices at once.