title: SKAudioNode positional audio seems to not work
body: <p>I'm trying to implement the "3d" audio Apple has added to SpriteKit, but the sounds really don't seem to be positioned at all, even with headphones on. Here's my relevant code.</p>
  
  <p>Play Sound function:</p>
  
  <pre><code>func playTapSound(node: SKNode) {
      let tapSound = SKAudioNode(fileNamed: "glassNote")
      tapSound.positional = true
      tapSound.autoplayLooped = false
      node.addChild(tapSound)
      tapSound.runAction(SKAction.play())
  }
  </code></pre>
  
  <p>Game Scene:</p>
  
  <pre><code>let listenerNode = SKNode()
  ...
  override func didMoveToView(view: SKView) {
      listenerNode.position = view.center
      listener = listenerNode
  }
  </code></pre>
  
  <p><code>playTapSound</code> gets called if the user taps a game piece node. </p>
  
  <pre><code>override func touchesBegan(touches: Set&lt;UITouch&gt;, withEvent event: UIEvent?) {
      let touchedNode = scene.nodeAtPoint(sceneTouchPoint)
      playTapSound(touchedNode)
  }
  </code></pre>
  
  <p>I've checked the positions of all the nodes including the listener node and they're all correct. Listener node is in the center of the screen and the game pieces are basically a checkerboard layout.</p>
  
  <p>When I tap a piece, I really can't tell there's any sort of positioning on the audio. Is it just extremely subtle? Can't find much info out there about it except Apple saying it's part of SpriteKit..</p>