Hi Samuel,
The term round-robin always makes me think of modulo arithmetic — the kind of arithmetic that works on a clock that wraps around at 12. So in your Sound, I would try the following in the Selection field:
(!KeyDown countTriggersMod: 3) + 1
This will give you a repeating pattern that selects your MultiSamples one after the other and repeats after the third one: 1, 2, 3, 1, 2, …
Alternatively, you could get rid of the SelectableSound and put all three MultiSamples into the MIDIVoice. Then, in the Gate field of the first MultiSample, you could use:
!KeyDown gateWhen: ((!KeyDown countTriggersMod: 3) eq: 0)
and in the second MultiSample Gate field:
!KeyDown gateWhen: ((!KeyDown countTriggersMod: 3) eq: 1)
and so on. That expression would gate the MultiSamples in order (and each of your MultiSamples is, in turn, selecting a sample based on its base pitch).
Following your lead, I’ll conclude with Pete’s catch-phrase: “Hope it makes sense”