SynthDef.new(\testSynth, {  |bufnum|
  var pb;
  pb = PlayBuf.ar(
    numChannels: 2,
    rate: BufRateScale.kr(bufnum),
    bufnum: bufnum,
    doneAction: 3,
  );
  Out.ar(1, pb);
}).add;

~group = Group.new;
~nSeconds = 3;
~oneSecond = s.sampleRate;
~buf = Buffer.alloc(s, ~oneSecond * ~nSeconds, numChannels: 2);

SystemClock.sched(~nSeconds + 0.01, {
  ("System clock done in" + ~nSeconds + "seconds").postln;
  ~group.dumpTree;
});
Synth.new("testSynth", args: [\bufnum, ~buf.bufnum], target: ~group);