AudioKit ios AKSamplerMetronome

Question

我目前正在使用AudioKit的AKSamplerMetronome来生成和播放Metronome的声音，现在我需要实现一个回调来获得当前的节拍，假设我有5个节拍，我需要播放当前的节拍，这样我就可以在节拍计数的基础上添加更多的功能，有什么可以实现的回调吗？

这是我目前的代码

 // using AKSamplerMetronome
var metronome1 = AKSamplerMetronome()
var mixer = AKMixer()
// first sound called
let beatstart = Bundle.main.url(forResource: "mybeat", withExtension: "wav")
 // other sounds based on beat count
let beaten = Bundle.main.url(forResource: "others", withExtension: "wav")
// setting first sound and other beat sounds
metronome1.sound = McountSoundUrl
metronome1.downBeatSound = MoneSoundUrl
metronome1 >>> mixer
AudioKit.output = mixer
AudioKit.start()

Answer 1

您可以很轻松地使用AKSequencer (我做了类似的事情)。我给AKMIDISampler分配了一个音轨，产生节拍器的声音，第二个音轨则指向一个AKCallbackInstrument。

在发送给AKCallbackInstrument的磁道中，我在MIDI数据中任意编码了拍频信息，因此，例如，MIDI数据的第一个节拍的MIDINote为1，第二个为MIDINote 2(您可以用速度来实现这一点)。然后，回调函数只需查看所有的noteOn消息，并从MIDI编号中获取当前的节拍，并相应地做出响应。这有点间接，但有效。

// create the sequencer before hand (e.g., at init); calling play() immediately after creating it causes some odd behaviour
    let sequencer = AKSequencer()

    // set up the sampler and callbackInst
    let sampler = AKSynthSnare()
    // or for your own sample:
    // let sampler = AKMIDISampler()
    // sampler.loadWav("myMetronomeSound)
    let callbackInst = AKCallbackInstrument()
    AudioKit.output = sampler
    AudioKit.start()

    // create two tracks for the sequencer
    let metronomeTrack = sequencer.newTrack()
    metronomeTrack?.setMIDIOutput(sampler.midiIn)
    let callbackTrack = sequencer.newTrack()
    callbackTrack?.setMIDIOutput(callbackInst.midiIn)

    // create the MIDI data
    for i in 0 ..< 4 {
        // this will trigger the sampler on the four down beats
        metronomeTrack?.add(noteNumber: 60, velocity: 100, position: AKDuration(beats: Double(i)), duration: AKDuration(beats: 0.5))

        // set the midiNote number to the current beat number
        callbackTrack?.add(noteNumber: MIDINoteNumber(i), velocity: 100, position: AKDuration(beats: Double(i)), duration: AKDuration(beats: 0.5))
    }

    // set the callback
    callbackInst.callback = {status, noteNumber, velocity in
        guard status == .noteOn else { return }
        print("beat number: \(noteNumber + 1)")
        // e.g., resondToBeat(beatNum: noteNumber)
    }

    // get the sequencer ready
    sequencer.enableLooping(AKDuration(beats: 4))
    sequencer.setTempo(60)
    sequencer.play()