在AudioQueueBuffers之間彈出噪音

Question

我正在嘗試使用Core Audio AudioQueue的（Swift 3）播放純正弦波音調。

它的播放效果很好，但是每次我的AudioQueueOutputCallback調用以用音頻數據填充新緩沖區時，我都會突然發出雜音。

我的AudioStreamer類如下所示：

let kNumberBuffers = 3

protocol AudioStreamerDelegate {
    func requestAudioData() -> [Float]
}

let sampleRate = 48000.0
let bufferSize = Int(sampleRate) / 50
let bufferByteSize = UInt32(bufferSize * sizeof(Float)) // 20 mili sec of audio

class AudioStreamer {
    var delegate: AudioStreamerDelegate

    var outputQueue: AudioQueueRef?

    var buffers = [AudioQueueBufferRef?](repeatElement(nil, count: kNumberBuffers))

    var streamBasicDescription = AudioStreamBasicDescription(
        mSampleRate: sampleRate,
        mFormatID: kAudioFormatLinearPCM,
        mFormatFlags: kAudioFormatFlagsNativeFloatPacked | kAudioFormatFlagIsNonInterleaved,
        mBytesPerPacket: UInt32(sizeof(Float)),
        mFramesPerPacket: 1,
        mBytesPerFrame: UInt32(sizeof(Float)),
        mChannelsPerFrame: 1,
        mBitsPerChannel: UInt32(8 * sizeof(Float)),
        mReserved: 0
    )

    init(delegate: AudioStreamerDelegate) {
        // create new output audio queue
        self.delegate = delegate
    }

    func play() {
        let queue = DispatchQueue.main

        queue.async(execute: {
            let selfPointer = unsafeBitCast(self, to: UnsafeMutablePointer<Void>.self)
            AudioQueueNewOutput(
                &self.streamBasicDescription,
                AudioStreamerOuputCallback,
                selfPointer,
                nil,
                nil,
                0,
                &self.outputQueue
            )

            // allocate buffers
            for i in 0 ..< kNumberBuffers {
                AudioQueueAllocateBuffer(
                    self.outputQueue!,
                    bufferByteSize,
                    &self.buffers[i]
                )

                if let bufferRef = self.buffers[i] {
                    // configure audio buffer
                    let selfPointer = unsafeBitCast(self, to: UnsafeMutablePointer<Void>.self)
                    bufferRef.pointee.mUserData = selfPointer
                    bufferRef.pointee.mAudioDataByteSize = bufferByteSize
                }
            }

            AudioQueuePrime(self.outputQueue!, 0, nil)
            for bufferRef in self.buffers {
                AudioStreamerOuputCallback(userData: unsafeBitCast(self, to: UnsafeMutablePointer<Void>.self), queueRef: self.outputQueue!, buffer: bufferRef!)
            }
            AudioQueueStart(self.outputQueue!, nil)
        })
    }
}

func AudioStreamerOuputCallback(userData: Optional<UnsafeMutablePointer<Void>>, queueRef: AudioQueueRef, buffer: AudioQueueBufferRef) {
    let this = Unmanaged<AudioStreamer>.fromOpaque(OpaquePointer(userData!)).takeUnretainedValue()
    let audioData = this.delegate.requestAudioData()

    memcpy(buffer.pointee.mAudioData, unsafeBitCast(audioData, to: UnsafeMutablePointer<Void>.self), Int(bufferByteSize))
    AudioQueueEnqueueBuffer(queueRef, buffer, 0, nil)
}

僅帶有“播放”按鈕的ViewController類的音頻數據生成器方法（theta是該ViewController上的存儲屬性）：

func generateAudioData(frequency: Double) {
    semaphore.wait()

    let amplitude: Double = 0.25

    let theta_increment: Double = 2.0 * M_PI * frequency / sampleRate

    for j in 0 ..< Int(bufferSize) {
        audioData[j] = Float(sin(theta) * amplitude)
        theta += theta_increment

        if theta > 2.0 * M_PI {
            theta -= 2.0 * M_PI
        }
    }
}

該問題看起來類似於該問題 ，但沒有人回答。

任何幫助將不勝感激。

Answer 1

在輸出回調中，您沒有生成新的音頻數據集，其中新緩沖區的第一個樣本的相位是前一個緩沖區的最后一個樣本的增量。