Swift AudioKit：如何构建音高由 AR 包络控制的 VCO？

Question

我是 AudioKit 新手。我想构建一个音高由可重新触发的 A(H)R 包络（衰减可调）控制的 VCO，我正在寻找最好或最常见的方法来实现它。

经过一些研究 () 在我看来，我必须使用 AKOperationGenerator 和 AKOperation。

我试过了：

enum PitchEnvVCOSynthParameter: Int {
    case frequency, decayTime, gate
}

struct PitchEnvVCO {
    static var frequency: AKOperation {
        return AKOperation.parameters[PitchEnvVCOSynthParameter.frequency.rawValue]
    }
    static var decayTime: AKOperation {
        return AKOperation.parameters[PitchEnvVCOSynthParameter.decayTime.rawValue]
    }
    static var gate: AKOperation {
        return AKOperation.parameters[PitchEnvVCOSynthParameter.gate.rawValue]
    }
}

extension AKOperationGenerator {
    var frequency: Double {
        get { return self.parameters[PitchEnvVCOSynthParameter.frequency.rawValue] }
        set(newValue) { self.parameters[PitchEnvVCOSynthParameter.frequency.rawValue] = newValue }
    }
    var decayTime: Double {
        get { return self.parameters[PitchEnvVCOSynthParameter.decayTime.rawValue] }
        set(newValue) { self.parameters[PitchEnvVCOSynthParameter.decayTime.rawValue] = newValue }
    }
    var gate: Double {
        get { return self.parameters[PitchEnvVCOSynthParameter.gate.rawValue] }
        set(newValue) { self.parameters[PitchEnvVCOSynthParameter.gate.rawValue] = newValue }
    }
}

和

class SimpleGenerator: AKNode {

    var generator = AKOperationGenerator { parameters in

        var oscillator = AKOperation.squareWave(frequency: PitchEnvVCO.frequency.triggeredWithEnvelope(
           trigger: PitchEnvVCO.gate,
           attack: 0.01,
           hold: 0.01,
           release: 0.2
        )).triggeredWithEnvelope(trigger: PitchEnvVCO.gate, attack: 0.1, hold: 0.01, release: 0.5)

        return oscillator
    }

    var vco1Freq: Double = 440.0 {
        didSet {
            generator.parameters[PitchEnvVCOSynthParameter.frequency.rawValue] = vco1Freq
        }
    }

    var pitchDecay: Double = 0.1 {
        didSet {
            generator.parameters[PitchEnvVCOSynthParameter.decayTime.rawValue] = pitchDecay
        }
    }
    var sourceMixer = AKMixer()

    func start() {
        generator.parameters = [vco1Freq, pitchDecay, 0] // Initialize the array
        generator.start()
    }

    func triggerGate(_ freq: Double) {
        vco1FreqOffset = freq
        generator.parameters[PitchEnvVCOSynthParameter.gate.rawValue] = 1
        // or generator.trigger(1)
    }

    override init() {
        sourceMixer = AKMixer(generator)
        super.init()
        avAudioNode = sourceMixer.avAudioNode
    }
}

我通过音序器轨道触发发生器，触发回调

let seqPositioncallbackTrack = sequencer.newTrack()
seqPositioncallbackTrack?.setMIDIOutput(sequencerCallbackInst.midiIn)
sequencerCallbackInst.callback = { status, noteNumber, velocity in
    self.onSequencerStepChange(status: status, noteNumber: noteNumber, velocity: velocity)
}
//...for i in 0 ..< numberOfSteps...etc.
seqPositioncallbackTrack?.add(noteNumber: MIDINoteNumber(i), 
    velocity: 100, 
    position: AKDuration(beats: Double(i)), 
    duration: AKDuration(beats: 0.5)
)

效果很好。但我只听到无尽的声音（频率正确）。只有第一个触发器在音高中膨胀。其他触发器不会重新触发包络。怎么会-我错了什么？ THNX

Answer 1

看来我需要找到 gate-on 时间的正确长度（注意音序器步进持续时间的长度），并发送一个 gate-off 事件以将门设置为零。

...duration: AKDuration(seconds: 0.03)


private func onSequencerStepChange(status: AKMIDIStatus, noteNumber: MIDINoteNumber, velocity: MIDIVelocity) {

    if status == .noteOn {
        core.triggerGateOn(seq1Values[Int(noteNumber)])
    }
    else if status == .noteOff {
        core.triggerGateOff()
    }
    else { return }

}
...
// splitting func triggerGate(_ freq: Double) into on/off:
func triggerGateOn(_ freq: Double) {
    generator.parameters[PitchEnvVCOSynthParameter.gate.rawValue] = 1
}

func triggerGateOff() {
    generator.parameters[PitchEnvVCOSynthParameter.gate.rawValue] = 0
}

当持续时间太短时它似乎也不起作用，意味着 < 0.03 - 那么我猜 gate-on 设置为关闭比攻击时间结束更快。还有我不得不使用释放时间来模拟的衰减时间

let generator = AKOperationGenerator { parameters in

    let oscillator = AKOperation.squareWave(
        frequency: PitchEnvVCO.frequency.triggeredWithEnvelope(
            trigger: PitchEnvVCO.gate,
            attack: 0.01,
            hold: 0.0,
            release: PitchEnvVCO.freqDecayTime
        ),
        amplitude: PitchEnvVCO.amplitude.triggeredWithEnvelope(
            trigger: PitchEnvVCO.gate,
            attack: 0.01,
            hold: 0.0,
            release: PitchEnvVCO.ampDecayTime
        )
    )
    return oscillator
}

编辑：好的 - 我找到的正确答案已发布

Swift AudioKit：如何构建音高由 AR 包络控制的 VCO？

Swift AudioKit: How to build an VCO who's pitch is controlled by an AR-envelope?

ios

swift

audiokit

akoperationgenerator