title: AVAudioMixerNode pan or AVAudioUnitSampler stereoPan properties not working to change left/right balance of sound output for AVAudioEngine
body: <p>I have the following code, which plays a single midi note, but I want to be able to adjust the balance/pan so that it only plays out of the left speaker or the right speaker or perhaps some combination. I thought changing "sampler.stereoPan" or perhaps "engine.mainMixerNode.pan" would do the trick but it seems to have no effect. Any ideas what I'm doing wrong?</p>
  
  <pre><code>engine = AVAudioEngine()
  sampler = AVAudioUnitSampler()
  
  sampler.stereoPan = -1.0 // doesn't work
  //engine.mainMixerNode.pan = -1.0 // doesn't work
  
  engine.attachNode(sampler)
  engine.connect(sampler, to: engine.mainMixerNode, format: engine.mainMixerNode.outputFormatForBus(0))
  
  var error: NSError?
  engine.startAndReturnError(&amp;error)
  
  sampler.startNote(65, withVelocity: 64, onChannel: 1)
  </code></pre>