title: AudioKit 4.6 release: AKMIDICallbackInstrument not calling back
body: <p>Really excited by all the additions in 4.6! After reviewing most of the changes, I did not see anything explicitly different in <code>AKMIDICallbackInstrument</code>, however, I cannot get the call back to work anymore. Here is my implementation:</p>
  
  <pre><code>var sequencer: AKSequencer = AKSequencer()
  var callbackTrack: AKMusicTrack = AKMusicTrack()
  var callbackInst: AKMIDICallbackInstrument = AKMIDICallbackInstrument() 
  
  ---
  
  public func setupSequencerWithBeats(beats: Int, bpm: Double) {
  
      print("Num beats: \(beats) | BPM: \(bpm)")
      sequencer.setTempo(bpm)
  
      callbackTrack = sequencer.newTrack()!
      callbackTrack.setMIDIOutput(callbackInst.midiIn)
  
      for i in 0 ..&lt; beats {
          callbackTrack.add(noteNumber: MIDINoteNumber(60), velocity: 100, position: AKDuration(beats: Double(i)), duration: AKDuration(beats: 1))
          }
  
      callbackInst.callback = {status, noteNumber, velocity in
  
          //Using the new AKMIDIStatus object to unwrap the status and check if it's .noteOn
          if let midiStatus = AKMIDIStatus(byte: status), midiStatus.type != .noteOn
              {
                  return
              }
  
          // just some delegates to other classes                 
          self.sequencerdDelegate?.didRecieveCallbackFromSequencer(beatNumber: self.beatNumber)
          self.beatNumber += 1
      }
  </code></pre>
  
  <p>When I call <code>sequencer.play()</code> the <code>callbackInst</code> fails to fire the callback anymore. My assumption here is did something change with <code>setMIDIOutput()</code> method? If there is a better way to get a callback when a .noteOn event is fired in my sequencer, I would love to know. Thanks everyone!</p>