Xcode 8 Swift 3 种改变音高的声音

Question

我正在尝试制作一款简单的游戏，当你击中某物时，它的音高会有所不同。我以为这很简单，但结果却有很多东西（其中大部分是我完全从别人那里复制的）：

func hitSound(value: Float) {  
 
    let audioPlayerNode = AVAudioPlayerNode()  
 
     audioPlayerNode.stop()  
     engine.stop() // This is an AVAudioEngine defined previously  
     engine.reset()  
 
     engine.attach(audioPlayerNode)  
 
     let changeAudioUnitTime = AVAudioUnitTimePitch()  
     changeAudioUnitTime.pitch = value  
 
     engine.attach(changeAudioUnitTime)  
     engine.connect(audioPlayerNode, to: changeAudioUnitTime, format: nil)  
     engine.connect(changeAudioUnitTime, to: engine.outputNode, format: nil)  
     audioPlayerNode.scheduleFile(file, at: nil, completionHandler: nil) // File is an AVAudioFile defined previously  
     try? engine.start()  
 
     audioPlayerNode.play()  
 }

由于此代码似乎停止播放当前正在播放的任何声音以播放新声音，是否有办法改变此行为，使其不停止播放任何内容？我尝试删除 engine.stop 和 engine.reset 位，但这只会使应用程序崩溃。此外，这段代码在频繁调用时速度非常慢。我可以做些什么来加快速度吗？经常需要这个命中音

Answer 1

每次播放声音都在重置引擎！而且您正在创建额外的播放器节点 - 如果您只想同时播放一个音高偏移声音实例，这实际上比这要简单得多：

// instance variables
let engine = AVAudioEngine()
let audioPlayerNode = AVAudioPlayerNode()
let changeAudioUnitTime = AVAudioUnitTimePitch()

调用 setupAudioEngine() 一次：

func setupAudioEngine() {
    engine.attach(self.audioPlayerNode)

    engine.attach(changeAudioUnitTime)
    engine.connect(audioPlayerNode, to: changeAudioUnitTime, format: nil)
    engine.connect(changeAudioUnitTime, to: engine.outputNode, format: nil)
    try? engine.start()
    audioPlayerNode.play()
}

并多次调用 hitSound()：

func hitSound(value: Float) {
    changeAudioUnitTime.pitch = value

    audioPlayerNode.scheduleFile(file, at: nil, completionHandler: nil) // File is an AVAudioFile defined previously
}

p.s。音高可上下移动两个八度，范围为4个八度，数值范围为[-2400, 2400]，单位为"cents"。

p.p.s AVAudioUnitTimePitch 很酷的技术。我们小时候绝对没有这样的东西。

更新

如果你想要多通道，你可以很容易地设置多个播放器和音调节点，但是你必须在启动引擎之前选择通道数。下面是你如何做两个（很容易扩展到 n 个实例，你可能想选择你自己的方法来选择在所有播放时中断哪个频道）：

// instance variables
let engine = AVAudioEngine()
var nextPlayerIndex = 0
let audioPlayers = [AVAudioPlayerNode(), AVAudioPlayerNode()]
let pitchUnits = [AVAudioUnitTimePitch(), AVAudioUnitTimePitch()]

func setupAudioEngine() {
    var i = 0
    for playerNode in audioPlayers {
        let pitchUnit = pitchUnits[i]

        engine.attach(playerNode)
        engine.attach(pitchUnit)
        engine.connect(playerNode, to: pitchUnit, format: nil)
        engine.connect(pitchUnit, to:engine.mainMixerNode, format: nil)

        i += 1
    }

    try? engine.start()

    for playerNode in audioPlayers {
        playerNode.play()
    }
}

func hitSound(value: Float) {
    let playerNode = audioPlayers[nextPlayerIndex]
    let pitchUnit = pitchUnits[nextPlayerIndex]

    pitchUnit.pitch = value

    // interrupt playing sound if you have to
    if playerNode.isPlaying {
        playerNode.stop()
        playerNode.play()
    }

    playerNode.scheduleFile(file, at: nil, completionHandler: nil) // File is an AVAudioFile defined previously

    nextPlayerIndex = (nextPlayerIndex + 1) % audioPlayers.count
}

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