CODEWITHSUNDEEP
iosswiftxcodeaudioinverse
Saif Ali
Saif Ali

Reputation: 427

How to Generate Phase Inverse audio file from input audio file in Swift?

I am recording sound through audio engine and make a file name my_file.caf and trying to make another file which will make its phase inverse that i can cancel its voice in mono.

But when I do some operations and calculations it reversed its sin wave but also reverse the sound.

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)        
}

I have tried all possible ways and I'm stuck so can someone help?

Upvotes: 1

Views: 386

Answers (1)

HaraldCoder
HaraldCoder

Reputation: 71

My naive approach would be: subtract the average (the bias), multiply by -1, add average back in.

Upvotes: 2

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