AudioKit: How to operate with AKOperation parameter values as Double?

Question

I want to calculate pow() in the following context:

let generator = AKOperationGenerator { parameters in

    let depth = PitchEnvVCO.freqDecayDepth.times(PitchEnvVCO.freqDecayAmount)
    let wdth = pow(2.0, depth/12.0) * PitchEnvVCO.frequency // throws error
    let ptch = AKOperation.exponentialSegment(
        trigger: PitchEnvVCO.gate,
        start: wdth,
        end: PitchEnvVCO.frequency,
        duration: PitchEnvVCO.freqDecayTime
    )

    let oscillator = AKOperation.squareWave(

        frequency: ptch,
        amplitude: PitchEnvVCO.amplitude.triggeredWithEnvelope(
            trigger: PitchEnvVCO.gate,
            attack: 0.01,
            hold: 0.0,
            release: PitchEnvVCO.ampDecayTime
        )
    )
    return oscillator
}

and get the error

Cannot convert value of type 'AKOperation' to expected argument type 'Double'

I have build my generator like in the filter envelope example. How could I cast AKOperation to its Double Value? thnx!

Answer 1

After rethinking the concept I did the calculation outside the AKOperationGenerator and added more AKOperation.parameters to store the results:

let generator = AKOperationGenerator { parameters in

    let ptch = AKOperation.exponentialSegment(
        trigger: PitchEnvVCO.gate,
        start: PitchEnvVCO.freqDecayDepth,
        end: PitchEnvVCO.frequency.plus(PitchEnvVCO.frequencyOffset),
        duration: PitchEnvVCO.freqDecayTime
    )

    let oscillator = AKOperation.morphingOscillator(
        frequency: ptch,
        amplitude: PitchEnvVCO.amplitude.triggeredWithEnvelope(
            trigger: PitchEnvVCO.gate,
            attack: 0.01,
            hold: 0.0,
            release: PitchEnvVCO.ampDecayTime
        ),
        index: 1 // square
    )
    return oscillator
}

func getFrequencyOffsetInHz() -> Double { // converts frequency in Hz from semitones
    // change n semitones relative to baseFreq : fn = 2power(n/12) × Fb
    return (pow(2, vco1FreqOffset/12) * vco1Freq) - vco1Freq
}

func getFreqModDepthInHz() -> Double{ // converts semintone depth to Hz
    let currentFrequency = vco1Freq + getFrequencyOffsetInHz()
    let powow = pow(2.0, (vco1EGAmnt * vco1DecayDepth)/12.0) * currentFrequency
    if powow != 0.0 {
        return powow
    }
    return currentFrequency
}

func setOscParamsForBaseFreq() {
    generator.parameters[PitchEnvVCOSynthParameter.frequency.rawValue] = vco1Freq
    generator.parameters[PitchEnvVCOSynthParameter.frequencyOffset.rawValue] = getFrequencyOffsetInHz()
    generator.parameters[PitchEnvVCOSynthParameter.freqDecayDepth.rawValue] = getFreqModDepthInHz()
}