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.