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I'm trying to use AudioKit to playback a sound on each beat of a measure(s). Although I've implemented the code from this similar question regarding callbacks via AudioKit, I can't seem to get the sequencer to update changes and playback properly. It will play once accurately, however after rewinding and changing the values it will only use the initial values (or not playback at all).

My intent is to create a struct of measures with beat values for each measure, then use MIDI and the callback to play different sounds dependent on how many measures/beats there are. Thanks!

import UIKit
import AudioKit

class ViewController: UIViewController {

let sequencer = AKSequencer()

let click = AKSynthSnare()
let callbackInst = AKCallbackInstrument()

// Create the struct that defines each line
struct Line {
    var name: String
    var measures: Int
    var beatsPerMeasure: Int
    func totalBeats() -> Int {
        return (measures * beatsPerMeasure)
    }
}

// Initialize intro line
var intro = Line(name: "Intro", measures: 0, beatsPerMeasure: 0)

// A function to create/update/playback the sequence on button press
func playBack() {

    let metronomeTrack = sequencer.newTrack()
    metronomeTrack?.setMIDIOutput(click.midiIn)
    let callbackTrack = sequencer.newTrack()
    callbackTrack?.setMIDIOutput(callbackInst.midiIn)

    for steps in 0 ... Int(measuresRowOneValue) {
        // this will trigger the sampler on the four down beats
        metronomeTrack?.add(noteNumber: 60, velocity: 100, position: AKDuration(beats: Double(steps)), duration: AKDuration(beats: 0.5))

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

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

        }
    }
}


@IBOutlet weak var rowOneLocationOne: UIImageView!
// Listener for UI display values
var measuresRowOneValue: Int = 0 {
    didSet {
        intro.measures = measuresRowOneValue
    }
}

@IBAction func rowOnePlusButton(_ sender: UIButton) {
    measuresRowOneValue += 1
}

@IBAction func rowOneMinusButton(_ sender: UIButton) {
    measuresRowOneValue -= 1
}

@IBAction func playbackStart(_ sender: UIButton) {
    playBack()
    sequencer.play()
}

@IBAction func playbackStop(_ sender: UIButton) {
    sequencer.stop()
}

@IBAction func playbackRestart(_ sender: UIButton) {
    sequencer.rewind()
}

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    AudioKit.output = click
    try!AudioKit.start()
}
}
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1 回答 1

4

您的代码中有一些令人困惑的事情，所以我不确定这是否是您唯一的问题，但至少，每次更改序列的长度时，您都需要setLength()调用enableLooping. 基本上，默认情况下（即，除非您明确设置长度）序列的长度将是序列中最长轨道的长度。在您的“播放”方法中，您在轨道顶部添加轨道而不删除旧轨道，因此它无法知道您希望序列持续多长时间。

您的“回放”方法正在做两件不同的事情（都不涉及回放）。你可能想打破它。你可以setup()做一些只需要做一次的事情（创建轨道，设置它们的输出，设置回调）和一个rewriteSequence()当你想重写轨道时被调用的方法。通过这种方式，您可以重复使用现有曲目，而不是不断创建新曲目。

var metronomeTrack: AKMusicTrack!
var callbackTrack: AKMusicTrack!

    // call this just once at the start
    func setup() {
        metronomeTrack = sequencer.newTrack()
        metronomeTrack?.setMIDIOutput(click.midiIn)
        callbackTrack = sequencer.newTrack()
        callbackTrack?.setMIDIOutput(callbackInst.midiIn)

        callbackInst.callback = {status, noteNumber, velocity in
            guard status == .noteOn else { return }
            print("beat number: \(noteNumber + 1)")

        }
    }

    // call this each time you want to change the sequence
    func rewriteSequence() {
        metronomeTrack?.clear()
        callbackTrack?.clear()
        for steps in 0 ... Int(measuresRowOneValue) {
            metronomeTrack?.add(noteNumber: 60, velocity: 100, position: AKDuration(beats: Double(steps)), duration: AKDuration(beats: 0.5))
            callbackTrack?.add(noteNumber: MIDINoteNumber(steps), velocity: 100, position: AKDuration(beats: Double(steps)), duration: AKDuration(beats: 0.5))
        }

        // This will make sure it loops correctly:
        sequencer.setLength(AKDuration(beats: Double(measuresRowOneValue)))
        sequencer.enableLooping()
    }

我希望这有帮助。

于 2018-05-31T12:43:39.183 回答