     // MARK: Properties
 
     /// All callbacks that will get triggered by MIDI events
-    public var callbacks = [AKMIDICallback]()
+    public var callback: AKMIDICallback?
 
     /// Initialize the callback instrument
     ///

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

    private func triggerCallbacks(status: AKMIDIStatus,
                                  noteNumber: MIDINoteNumber,
                                  velocity: MIDIVelocity) {
        if callback != nil {
            callback!(status, noteNumber, velocity)
        }
    }

