I can test a bit later, but I think this is cased out in the docs as possible:
engine.name = 'PolyPerc'
function forever(freq,rate)
while true do
clock.sync(1/rate)
engine.hz(freq)
end
end
function init()
voice = {}
voice[1] = clock.run(forever,333,3)
voice[2] = clock.run(forever,666,1)
voice[3] = clock.run(forever,999,2)
voice[4] = clock.run(forever,111,0.33)
end