Play Audio for a Metronome

Hi,

I am looking for a good way to play sounds at a high frequency. At the moment I am using the AVAudioEngine, and create a couple AVAudioPlayerNode and for each sound I need to play I create a AVAudioPCMBuffer.

When the app needs to play a sound, I get the correct AVAudioPCMBuffer for the sound and use the first available AVAudioPlayerNode and feed it to the buffer.

The timing for a metronome app has to be very precise because if it's of by about 16ms the user can hear that it is not playing had the right interval. For low speeds this is working without any problems, but at high speeds it is getting worse.

Maybe anyone has an idea on how I can improve my method.

Its a Plugin for Flutter.

import AVFoundation

class FastSoundPlayer {
    
    private var audioPlayers: [SoundPlayer?] = []
    private var sounds: [String: Sound] = [:]
    private var engine = AVAudioEngine()
    let session = AVAudioSession.sharedInstance()

    init() {
        do {
            try session.setCategory(AVAudioSession.Category.playback, mode: AVAudioSession.Mode.default, options: [AVAudioSession.CategoryOptions.mixWithOthers])
            try session.setActive(true)
            createSoundPlayers(count: 20)
            try engine.start()
        } catch {
            print("Error starting audio engine: \(error.localizedDescription)")
        }
    }

        // Selector method to handle applicationDidBecomeActiveNotification
        func applicationDidBecomeActive() {
            // Reinitialize AVAudioEngine and reattach all nodes
            do {
                engine.reset()
                objc_sync_enter(audioPlayers)
                audioPlayers.removeAll()
                createSoundPlayers(count: 20)
                objc_sync_exit(audioPlayers)
                try engine.start()
            } catch {
                print("Error starting audio engine: \(error.localizedDescription)")
            }
        }


    func createSoundPlayers(count: Int) {
        for _ in 0..<count {
            let player = SoundPlayer()
            engine.attach(player.player)
            engine.connect(player.player, to: engine.mainMixerNode, format: nil)
            audioPlayers.append(player)
        }
    }


    func load(sound: Data, name: String) {
            let sound = Sound(soundData: sound)
            sounds[name] = sound
    }

    func play(name: String) {
        if !engine.isRunning {
            applicationDidBecomeActive()
        }
        guard let sound = sounds[name] else {
            print("Sound not found")
            return
        }
        if let player = getAvailablePlayer() {
            player.play(sound: sound)
        }
    }
    
    func getAvailablePlayer() -> SoundPlayer? {
        for player in audioPlayers {
            if !player!.isPlaying {
                return player
            }
        }
        return nil
    }
}

class SoundPlayer {
    let player = AVAudioPlayerNode()
    var isPlaying = false

    init() {
        player.volume = 1.0
    }


    func play(sound: Sound) {
        player.scheduleBuffer(sound.sound!, at: nil, options: .interrupts, completionCallbackType: .dataPlayedBack) { _ in
            self.complete()
            }
            if (player.engine != nil && player.engine!.isRunning) {
               player.play()
               isPlaying = true
             }
    }

    func complete() {
        isPlaying = false
    }

}

class Sound {
    var sound: AVAudioPCMBuffer?

    init(soundData: Data) {
                do {
            let temporaryURL = FileManager.default.temporaryDirectory.appendingPathComponent("tempSound.wav")
            try soundData.write(to: temporaryURL)

            // Create AVAudioFile from the temporary file URL
            let audioFile = try AVAudioFile(forReading: temporaryURL)

            // Define the format for the PCM buffer (44100Hz, stereo)
            let format = AVAudioFormat(commonFormat: .pcmFormatInt16, sampleRate: 44100, channels: 2, interleaved: false)

            // Create AVAudioPCMBuffer
            guard let pcmBuffer = AVAudioPCMBuffer(pcmFormat: format!, frameCapacity: AVAudioFrameCount(audioFile.length)) else {
                // Failed to create PCM buffer
                self.sound = nil
                return
            }

            // Read audio file into PCM buffer
            try audioFile.read(into: pcmBuffer)

            // Assign the created AVAudioPCMBuffer to the sound property
            self.sound = pcmBuffer
            } catch {
                print("Error loading sound file: \(error.localizedDescription)")
                self.sound = nil
            }
}
}

Thanks!