Swift: Sound-Output & Microphone-Input | using AudioKit |

问题

I'm using >Xcode Version 9.2<
I'm using >AudioKit Version 4.0.4<

I've written some code you can find below that should be able to

play a specific sound (frequency: 500.0HZ)
"listen" to the microphone input and calculating the frequency in real time

If I'm calling playSound() or receiveSound() separated everything looks fine and is really working as I expected. But calling playSound() and receiveSound() afterwards? Exactly there I got big issues.

This is how I'd like to get the code working:

SystemClass.playSound() //play sound
DispatchQueue.main.asyncAfter(deadline: (DispatchTime.now() + 3.0)) {
   SystemClass.receiveSound() //get microphone input 3 seconds later
}

let SystemClass: System = System()
class System {
    public init() { }

    func playSound() {
        let sound = AKOscillator()
        AudioKit.output = sound
        AudioKit.start()
        sound.frequency = 500.0
        sound.amplitude = 0.5
        sound.start()
        DispatchQueue.main.asyncAfter(deadline: (DispatchTime.now() + 2.0)) {
            sound.stop()
        }
    }


    var tracker: AKFrequencyTracker!
    func receiveSound() {
        AudioKit.stop()
        AKSettings.audioInputEnabled = true
        let mic = AKMicrophone()
        tracker = AKFrequencyTracker(mic)
        let silence = AKBooster(tracker, gain: 0)
        AudioKit.output = silence
        AudioKit.start()
        Timer.scheduledTimer( timeInterval: 0.1, target: self, selector: #selector(SystemClass.outputFrequency), userInfo: nil, repeats: true)
    }

    @objc func outputFrequency() {
        print("Frequency: \(tracker.frequency)")
    }
}

These messages are some of the compiler error-messages I get every time I'd like to run the code (calling playSound() and calling receiveSound () 3 seconds later):

AVAEInternal.h:103:_AVAE_CheckNoErr: [AVAudioEngineGraph.mm:1266:Initialize: (err = AUGraphParser::InitializeActiveNodesInOutputChain(ThisGraph, kOutputChainOptimizedTraversal, *GetOutputNode(), isOutputChainActive)): error -10875

AVAudioEngine.mm:149:-[AVAudioEngine prepare]: Engine@0x1c401bff0: could not initialize, error = -10875

[MediaRemote] [AVOutputContext] WARNING: AVF context unavailable for sharedSystemAudioContext

[AVAudioEngineGraph.mm:1266:Initialize: (err = AUGraphParser::InitializeActiveNodesInOutputChain(ThisGraph, kOutputChainOptimizedTraversal, *GetOutputNode(), isOutputChainActive)): error -10875

Fatal error: AudioKit: Could not start engine. error: Error 

Domain=com.apple.coreaudio.avfaudio Code=-10875 "(null)" UserInfo={failed call=err = AUGraphParser::InitializeActiveNodesInOutputChain(ThisGraph, kOutputChainOptimizedTraversal, *GetOutputNode(), isOutputChainActive)}.: file /Users/megastep/src/ak/AudioKit/AudioKit/Common/Internals/AudioKit.swift, line 243

回答1:

I believe the lionshare of your problems are due to local declaration of AKNodes within the functions that use them:

   let sound = AKOscillator()
   let mic = AKMicrophone()        
   let silence = AKBooster(tracker, gain: 0)

Declare these as instance variables instead, as described here.

来源：https://stackoverflow.com/questions/48130457/swift-sound-output-microphone-input-using-audiokit

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