IODesc describes an input or output of a SynthDesc, as returned by SynthDesc: -outputs and SynthDesc: -inputs
A Symbol for the rate.
The number of channels.
This can either be a String, a Float or an UGen.
|String||The name of the control that provides the bus index|
|Float||A hard-coded bus index|
|UGen||The UGen providing the bus index|
The class of the input/output ugen, like In, Out, ReplaceOut, etc.