AudioKit: MIDICallbackInstrument not triggering a callback when triggered from Sequencer

Question

I'm trying to get a callback when a midi note is triggered so I can display a graphical representation of the current beat in the bar. Nothing I do seems to callback. This is the simplest version of the code that I have tried - audio plays back fine but the callback is never triggered. I have enabled Audio in Background Modes.

Here is the code:

class ViewMain: UIViewController {

    let engine = AudioEngine()
    let kicks = Sampler()
    let claps = Sampler()
    let sequencer = Sequencer()
    let mixer = Mixer()

    let midiCallbackInstrument = MIDICallbackInstrument()

    override func viewDidLoad() {
        super.viewDidLoad()
        
        midiCallbackInstrument.callback = myCallBack
        
        mixer.addInput(midiCallbackInstrument)
        mixer.addInput(kicks)
        mixer.addInput(claps)
        
        engine.output = mixer
        do {
            try engine.start()
        } catch {
            Log("AudioKit did not start! \(error)")
        }
        
        kicks.unloadAllSamples()
        claps.unloadAllSamples()
        
        guard let url = Bundle.main.resourceURL?.appendingPathComponent("SamplesSFZ/sfz/909A.sfz") else { return }
        kicks.loadSFZ(url: url)
        
        guard let url = Bundle.main.resourceURL?.appendingPathComponent("SamplesSFZ/sfz/909B.sfz") else { return }
        claps.loadSFZ(url: url)
        
        sequencer.addTrack(for: midiCallbackInstrument)
        
        sequencer.tracks[0].add(noteNumber: 36, velocity: 120, channel: 0, position: 0.0, duration: 1.0)
        sequencer.tracks[0].add(noteNumber: 37, velocity: 120, channel: 1, position: 0.5, duration: 1.0)
        sequencer.tracks[0].add(noteNumber: 38, velocity: 120, channel: 2, position: 1.0, duration: 1.0)
        sequencer.tracks[0].add(noteNumber: 39, velocity: 120, channel: 3, position: 0.5, duration: 1.0)
        sequencer.tracks[0].add(noteNumber: 40, velocity: 120, channel: 4, position: 2.0, duration: 1.0)
        sequencer.tracks[0].add(noteNumber: 41, velocity: 120, channel: 5, position: 0.5, duration: 1.0)
        sequencer.tracks[0].add(noteNumber: 42, velocity: 120, channel: 6, position: 3.0, duration: 1.0)
        sequencer.tracks[0].add(noteNumber: 43, velocity: 120, channel: 7, position: 0.5, duration: 1.0)
        
        sequencer.addTrack(for: kicks)
        sequencer.tracks[1].add(noteNumber: 24, velocity: 120, channel: 0, position: 0.0, duration: 2.0)

        sequencer.addTrack(for: claps)
        sequencer.tracks[2].add(noteNumber: 25, velocity: 120, channel: 0, position: 1.0, duration: 0.1)
        sequencer.tracks[2].add(noteNumber: 25, velocity: 120, channel: 0, position: 3.0, duration: 0.1)
        
        sequencer.loopEnabled = true
        sequencer.tempo = 120.0
        sequencer.length = 4.0
        
        sequencer.play()
    }

    func myCallBack(a: UInt8, b:MIDINoteNumber, c:MIDIVelocity) -> () {
        // THIS IS NEVER CALLED
        print("*** callback invoked")
    }
}

Thanks in advance - I really appreciate any help here.

You're sending the callback instrument as well as the sampler outputs to the mixer, but not the sequencer tracks themselves. Iirc, connecting the tracks is also necessary, see https://stackoverflow.com/a/61545391/2717159 — c_booth, Feb 08 '22 at 19:47
Many thanks for coming back! If I try: mixer.addInput( sequencer.addTrack(for: midiCallbackInstrument) ) it failesbecause a sequencer track is not a node, which is the expected type for a mixer input, which makes sense. Still no joy here. — domhawken, Feb 10 '22 at 23:33

Brian H · Answer 1 · 2022-03-25T21:43:36.820

I have had good results with the newer AudioKit CallbackInstrument, which is intended as a replacement for MIDICallbackInstrument.

 To get CallbackInstrument working with your code, you only need to make two changes:

// replace let midiCallbackInstrument = MIDICallbackInstrument() with

          var midiCallbackInstrument = CallbackInstrument()

// replace midiCallbackInstrument.callback = myCallBack with

    midiCallbackInstrument = CallbackInstrument(midiCallback: { [self] (event, beat, velocity) in
        myCallBack(a: event, b: beat, c: velocity) } )

CallbackInstrument is documented here: https://github.com/AudioKit/AudioKit/wiki/CallbackInstrument

and the Shaker Metronome recipe in the AudioKit Cookbook is an example of how it is used. https://github.com/AudioKit/Cookbook

score 0 · Answer 2 · edited Mar 16 '22 at 06:43

0

Use sequencer.setGlobalMIDIOutput(midiCallbackInstrument.midiIn) or sequencer.tracks[0].setMIDIOutput(midiCallbackInstrument.midiIn) to connect sequencer and midiCallbackInstrument.

edited Mar 16 '22 at 06:43

Stefano Sansone

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answered Mar 15 '22 at 08:58

zzxgbgba

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AudioKit: MIDICallbackInstrument not triggering a callback when triggered from Sequencer

2 Answers2