         super.init()
         let midi = AKMIDI()
         self.enableMIDI(midi.client, name: "callback midi in")
-        callbacks.append(callback)
+        self.callback = callback
         avAudioNode = AVAudioMixerNode()
         AudioKit.engine.attachNode(self.avAudioNode)
     }

    private func triggerCallbacks(status: AKMIDIStatus,
                                  noteNumber: MIDINoteNumber,
                                  velocity: MIDIVelocity) {
        for callback in callbacks {
            callback(status, noteNumber, velocity)
        }
    }


    // MARK: Properties

    /// All callbacks that will get triggered by MIDI events
    public var callback: AKMIDICallback?

    /// Initialize the callback instrument
    ///
