This gets the error

overtone.sc.machinery.ugen.sc_ugen.ControlProxy cannot be cast to
   java.lang.Number

@rudiwillalwaysloveyou you cant pass clojure number like that. You will need to pass it as buffer and use index:kr to get the number. You could write defn wrapper around your synth to do that.

There are other ways too, but defsynth is a compile time macro and the parameters are supercollider proxy types. So it corrolates to SynthDef in sc.

@rudiwillalwaysloveyou reading this again, the problem is not the number. You can of course pass number. I felt like you were trying to pass pre-calculated values. But the problem is ‘repeat’. The error message is misleading and needs to be improved. You need to find sc ugen that does repeat.