如何从 Swift 中的输入音频文件生成反相音频文件？

Question

我正在通过音频引擎录制声音并制作一个文件名 my_file.caf 并尝试制作另一个文件，这将使它的相位反转，我可以在单声道中取消它的声音。

但是当我进行一些运算和计算时，它反转了它的正弦波，同时也反转了声音。

do {
    let inFile: AVAudioFile = try AVAudioFile(forReading: URLFor(filename: "my_file.caf")!)
    let format: AVAudioFormat = inFile.processingFormat
    let frameCount: AVAudioFrameCount = UInt32(inFile.length)
    let outSettings = [AVNumberOfChannelsKey: format.channelCount,
                       AVSampleRateKey: format.sampleRate,
                       AVLinearPCMBitDepthKey: 16,
                       AVFormatIDKey: kAudioFormatMPEG4AAC] as [String : Any]

    let outFile: AVAudioFile = try AVAudioFile(forWriting: URLFor(filename: "my_file1.caf")!, settings: outSettings)
    let forwardBuffer: AVAudioPCMBuffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: frameCount)!
    let reverseBuffer: AVAudioPCMBuffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: frameCount)!

    try inFile.read(into: forwardBuffer)
    let frameLength = forwardBuffer.frameLength
    reverseBuffer.frameLength = frameLength
    let audioStride = forwardBuffer.stride

    for channelIdx in 0..<forwardBuffer.format.channelCount {
        let forwardChannelData = forwardBuffer.floatChannelData?.advanced(by: Int(channelIdx)).pointee
        let reverseChannelData = reverseBuffer.floatChannelData?.advanced(by: Int(channelIdx)).pointee

        var reverseIdx: Int = 0
        for idx in stride(from: frameLength, to: 0, by: -1) {
            memcpy(reverseChannelData?.advanced(by: reverseIdx * audioStride), forwardChannelData?.advanced(by: Int(idx) * audioStride), MemoryLayout<Float>.size)
            reverseIdx += 1
        }
    }
    try outFile.write(from: reverseBuffer)
} catch let error {
    print(error.localizedDescription)        
}

我已经尝试了所有可能的方法，但还是卡住了，有人可以帮忙吗？

Answer 1

我天真的方法是：减去平均值（偏差），乘以 -1，再加上平均值。

如何从 Swift 中的输入音频文件生成反相音频文件？

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