Ok here's the solution - well it doesn't answer my question but it gets the job done.

const var Sampler1 = Synth.getSampler("Sampler1"); const th = Engine.createTransportHandler(); th.setOnTempoChange(true, updateTimeStretchRatio); // fetch the current state const var obj = Sampler1.getTimestretchOptions(); // Apply your changes obj.SkipLatency = true; // Update the options Sampler1.setTimestretchOptions(obj); inline function updateTimeStretchRatio(newTempo) { local ratio = newTempo / 140; Sampler1.setTimestretchRatio(ratio); }