title: Crash when setting AudioKit output node on iPhone 5s
body: <p>I get a consistent crash whenever I set AudioKit output to a mixer node. The crash happens on an iPhone 5s running iOS 10.3.3, but NOT on an iPhone 7 running iOS 11.3.</p>
  
  <p>The code I'm running (setting up a recording view):</p>
  
  <pre><code>mic = AKMicrophone()
  mic.stop()
  fft = AKFFTTap.init(mic)
  micMixer = AKMixer(mic)
  micBooster = AKBooster(micMixer)
  micBooster.gain = 0
  do {
              recorder = try AKNodeRecorder(node: micMixer)
  
              if let file = recorder.audioFile {
                  player = try AKAudioPlayer(file: file)
                  player.looping = false
                  player.completionHandler = playingEnded
              }
              mainMixer = AKMixer(player, micBooster)
              AudioKit.output = mainMixer //THIS IS WHERE IT CRASHES!
          }
          catch {
              //debug prints here don't get printed
              throw error
          }
  </code></pre>
  
  <p>The catch block is never called, an error is not thrown.</p>
  
  <p>Crash details in logs:</p>
  
  <p>ERROR: [0x1b12c0b40] >avae> AVAudioIONodeImpl.mm:466: EnableBus_block_invoke: error -10849
  *** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'error -10849'</p>
  
  <p>Any help or information would be appreciated!</p>