我正在尝试使用加速框架在音频文件上执行FFT以查找频率。我从此问题中(可能是错误的)适应了代码:Spectrogram from AVAudioPCMBuffer using Accelerate framework in Swift。尽管'spectrum'的幅度可能为'0'、'inf'或'nan',而复数分割的'real'和'imag'成分打印出类似的结果;这表明这是问题的原因:'magnitude = sqrt(pow(real,2)+pow(imag,2))'。请纠正我,但我认为代码的其余部分没问题。为什么我会收到这些结果,我该如何解决它(分割组件应该是什么),我做错了什么?请记住,我对FFT和采样非常陌生,不知道如何为音频文件设置这个,所以任何帮助都将不胜感激。谢谢。以下是我正在使用的代码:
// get audio file
let fileURL:NSURL = NSBundle.mainBundle().URLForResource("foo", withExtension: "mp3")!
let audioFile = try! AVAudioFile(forReading: fileURL)
let fileFormat = audioFile.processingFormat
let frameCount = UInt32(audioFile.length)
let buffer = AVAudioPCMBuffer(PCMFormat: fileFormat, frameCapacity: frameCount)
let audioEngine = AVAudioEngine()
let playerNode = AVAudioPlayerNode()
audioMixerNode = audioEngine.mainMixerNode
let bufferSize = Int(frameCount)
let channels: NSArray = [Int(buffer.format.channelCount)]
let channelCount = channels.count
let floats1 = [Int(buffer.frameLength)]
for var i=0; i<channelCount; ++i {
channelSamples.append([])
let firstSample = buffer.format.interleaved ? i : i*bufferSize
for var j=firstSample; j<bufferSize; j+=buffer.stride*2 {
channelSamples[i].append(DSPComplex(real: buffer.floatChannelData.memory[j], imag: buffer.floatChannelData.memory[j+buffer.stride]))
}
}
// connect node
audioEngine.attachNode(playerNode)
audioEngine.connect(playerNode, to: audioMixerNode, format: playerNode.outputFormatForBus(0))
// Set up the transform
let log2n = UInt(round(log2(Double(bufferSize))))
let fftSetup = vDSP_create_fftsetup(log2n, Int32(kFFTRadix2))
// Create the complex split value to hold the output of the transform
// why doesn't this work?
var realp = [Float](count: bufferSize/2, repeatedValue: 0)
var imagp = [Float](count: bufferSize/2, repeatedValue: 0)
var output = DSPSplitComplex(realp: &realp, imagp: &imagp)
vDSP_ctoz(UnsafePointer(channelSamples), 2, &output, 1, UInt(bufferSize / 2))
// Do the fast Fourier forward transform
vDSP_fft_zrip(fftSetup, &output, 1, log2n, Int32(FFT_FORWARD))
// Convert the complex output to magnitude
var fft = [Float](count:Int(bufferSize / 2), repeatedValue:0.0)
let bufferOver2: vDSP_Length = vDSP_Length(bufferSize / 2)
vDSP_zvmags(&output, 1, &fft, 1, bufferOver2)
var spectrum = [Float]()
for var i=0; i<bufferSize/2; ++i {
let imag = output.imagp[i]
let real = output.realp[i]
let magnitude = sqrt(pow(real,2)+pow(imag,2))
spectrum.append(magnitude) }
// Release the setup
vDSP_destroy_fftsetup(fftSetup)
AVAudioPCMBuffer
内存的末尾索引。也许我要用修好的Swift 4版本替换这个答案。 - Rhythmic Fistman