Question

几天来，我一直在努力解决这个问题，但似乎找不到任何遇到相同问题或解决方法的人。

使用类别AVAudioSessionPlayAndRecord时，音频输出会在播放更高频率的声音（约16khz以上）时自发改变音量。这种移动会导致声音中的咔嗒声/失真。随附的是此现象的在线捕捉的屏幕截图。 Line-in capture

使用AVAudioPlayer，音频队列服务和AudioUnit可以观察到这种情况，并且仅在AVAudioSessionCategoryPlayAndRecord中发生。 AVAudioSessionCategoryPlayback可以按预期工作。

在iPhone7，iPhone 8和iPhone 10上已观察到此行为，并且在iPhone 6上进行的测试未显示该问题。

以下是使用Audio Queue Services的最小样本应用程序中的代码，它们以19.5khz和48khz的采样率播放正弦波。

对此有任何建议，我们将不胜感激。

struct outputData
{
    var phaseDiff: Double = (6.28318530717958 * 19500.0) / 48000.0
    var phase: Double = 0
}
var buffers: [AudioQueueBufferRef] = []
var queue: AudioQueueRef? = nil
var data = outputData()


override func viewDidLoad() {
    do{

        if #available(iOS 10.0, *) {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayAndRecord, mode: AVAudioSessionModeMeasurement, options: .defaultToSpeaker)
        } else {
            // Fallback on earlier versions
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayAndRecord, with: .defaultToSpeaker)
        }
        try AVAudioSession.sharedInstance().setActive(true)

    } catch let error as NSError {
        NSLog("Error setting up AVAudioSession: \(error)")
    }
    statusLabel.text = "Idle";
    setupAudioQueues()
}

var outputCallback: AudioQueueOutputCallback = {(
    inUserData: UnsafeMutableRawPointer?,
    inAQ: AudioQueueRef,
    inBuffer: AudioQueueBufferRef) -> Void in
    // Write out sine wave
    var data = inUserData!.assumingMemoryBound(to: outputData.self).pointee
    memset(inBuffer.pointee.mAudioData, 0, Int(inBuffer.pointee.mAudioDataBytesCapacity))
    inBuffer.pointee.mAudioDataByteSize = inBuffer.pointee.mAudioDataBytesCapacity

    let floatPtr = inBuffer.pointee.mAudioData.bindMemory(to: Float.self, capacity: Int(inBuffer.pointee.mAudioDataBytesCapacity))
    for i in 0 ..< inBuffer.pointee.mAudioDataBytesCapacity / 4
    {
        floatPtr[Int(i)] = Float(sin(data.phase) * 0.2)
        data.phase = fmod(data.phase + data.phaseDiff, 6.28318530717958 )
    }

    let status = AudioQueueEnqueueBuffer(inAQ, inBuffer, 0, nil)
    if(status != 0)
    {
        NSLog("Failed to enqueue buffer: \(status)")
    }
}

func setupAudioQueues()
{
    var queue: AudioQueueRef? = nil
    var streamDesc = AudioStreamBasicDescription.init(mSampleRate: 48000.0, mFormatID: kAudioFormatLinearPCM, mFormatFlags: kAudioFormatFlagIsFloat | kAudioFormatFlagIsPacked, mBytesPerPacket: 4, mFramesPerPacket: 1, mBytesPerFrame: 4, mChannelsPerFrame: 1, mBitsPerChannel: 32, mReserved: 0)
    let status = AudioQueueNewOutput(&streamDesc, outputCallback, &data, nil, nil, 0, &queue)

    if(status != 0)
    {
        NSLog("Failed to open new AudioQueueOutput: \(status)")
        return
    }

    for _ in 0..<3 {
        var buffer: AudioQueueBufferRef?
        AudioQueueAllocateBuffer(queue!, 4800, &buffer)
        outputCallback(&data, queue!, buffer!)
        if let buffer: AudioQueueBufferRef = buffer {
            buffers.append(buffer)
        }
    }

    self.queue = queue
}

@IBAction func playSineWave(_ sender: AnyObject) {
    DispatchQueue.main.async {
        self.statusLabel.text = "Playing Sine Wave";
    }
    if(continuePlaying)
    {
        return
    }
    AudioQueueStart(self.queue!, nil)

}

iOS-AVAudioSessionCategoryPlayAndRecord导致高频音频的音量变化

0 个答案: