Question

我正在使用以下代码来记录音频并生成幅度浮动数据。但是我不确定数据是否正确。有人可以验证吗？

用于录制音频的主程序类似于示例AudioQueueRecorder。

创建队列后，在其中添加callback和AudioQueueProcessingTapNew为：

guard let queue = queue else { return }        

var maxFrames : UInt32 = 0;
var tapFormat = AudioStreamBasicDescription()
var tap : AudioQueueProcessingTapRef? = nil
var player = MyInfo()

utils.checkError(AudioQueueProcessingTapNew(queue, tapCallback, &player, AudioQueueProcessingTapFlags.preEffects, &maxFrames, &tapFormat, &tap),
                 "Failed to create audio queue tap")

在tap回调（如上链接）中，我使用code来获取幅度：

let info = userData.assumingMemoryBound(to: MyInfo.self)
var sourceFlags: AudioQueueProcessingTapFlags = AudioQueueProcessingTapFlags(rawValue: 0)
var sourceNumFrames: UInt32 = 0
AudioQueueProcessingTapGetSourceAudio(tap, inNumFrames, ts, &sourceFlags, &sourceNumFrames, ioData)

print("ts:", ts.pointee)
print("num frames:", inNumFrames)

let numBuffers = ioData.pointee.mNumberBuffers
print("num buffers:", numBuffers)

if numBuffers > 0 {
    let numChans = ioData.pointee.mBuffers.mNumberChannels
    let size = ioData.pointee.mBuffers.mDataByteSize / 4 //Size of a float is 4
    let data: [Float] = Array(UnsafeMutableBufferPointer(start: ioData.pointee.mBuffers.mData!.assumingMemoryBound(to: Float.self), count: Int(size)))

    print("num chans:", numChans)
    print("size:", size)

    let fft = TempiFFT(withSize: Int(size), sampleRate: 44100.0)
    fft.windowType = TempiFFTWindowType.hamming
    fft.fftForward(data)
    fft.calculateLinearBands(minFrequency: 0, maxFrequency: fft.nyquistFrequency, numberOfBands: 20)

    var magnitudeArr = [Float](repeating: Float(0), count: 20)
    var magnitudeDBArr = [Float](repeating: Float(0), count: 20)
    for i in 0..<20 {
        magnitudeArr[i] = fft.magnitudeAtBand(i)
        //var magnitudeDB = TempiFFT.toDB(fft.magnitudeAtBand(i))
        log.debug("fft.magnitudeAtBand(\(i)) = \(fft.magnitudeAtBand(i))")
    }
}

我得到以下输出。我想画一个振幅图。

ts: AudioTimeStamp(mSampleTime: 359433.0, mHostTime: 7385045310414, mRateScalar: 0.9999903367259503, mWordClockTime: 4424786032, mSMPTETime: __C.SMPTETime(mSubframes: 0, mSubframeDivisor: 16384, mCounter: 0, mType: __C.SMPTETimeType, mFlags: __C.SMPTETimeFlags(rawValue: 1), mHours: 4800, mMinutes: 179, mSeconds: 1, mFrames: 0), mFlags: __C.AudioTimeStampFlags(rawValue: 7), mReserved: 28672)
num frames: 2048
num buffers: 2
num chans: 1
size: 2048
data: [-0.00013435386, 4.471163e-05, 2.5250512e-07, -0.00013112863, -4.2305917e-05, -6.0883203e-06, -6.9609705e-05, 1.3280656e-05, 2.6565194e-06, -7.048986e-05, -4.371278e-05, -0.00012498278, -0.00015581526, 2.6477476e-06, 0.00014767727, 0.00015129645, 0.0002481592, 0.00020998582, 7.0496775e-05, 0.00023169718, 0.00032023923, 9.4876516e-05, 3.0334933e-05, -0.00010365831, -0.00012052287, -3.4284778e-06, -8.221614e-05, -0.00013551829, -8.154745e-05, -8.845353e-06, -5.211319e-05, 6.356722e-05, 0.00014827582] ...

fft.magnitudeAtBand(0) = 0.0019885404
fft.magnitudeAtBand(1) = 0.0002433162
fft.magnitudeAtBand(2) = 0.00011211308
fft.magnitudeAtBand(3) = 0.00019586945
fft.magnitudeAtBand(4) = 0.00015595475
fft.magnitudeAtBand(5) = 1.6589744e-05
fft.magnitudeAtBand(6) = 0.0019934585
fft.magnitudeAtBand(7) = 0.00035403066
fft.magnitudeAtBand(8) = 0.0020195032
fft.magnitudeAtBand(9) = 0.0019526586
fft.magnitudeAtBand(10) = 0.0010482509
fft.magnitudeAtBand(11) = 0.0015899779
fft.magnitudeAtBand(12) = 0.00021513038
fft.magnitudeAtBand(13) = 8.8768e-05
fft.magnitudeAtBand(14) = 0.00088070636
fft.magnitudeAtBand(15) = 3.6925994e-05
fft.magnitudeAtBand(16) = 0.0013688633
fft.magnitudeAtBand(17) = 0.0020811968
fft.magnitudeAtBand(18) = 0.00039211413
fft.magnitudeAtBand(19) = 1.50605065e-05

stop record did tap

但是magnitudeAtBand值似乎很小。它是否正确？如何绘制振幅图？

在数据值中，有负数。为什么是负面的？

Answer 1

在OS X上，32位浮点样本的范围是-1.0f至1.0f。出现负数是因为（行的）样本描述了模拟波形信号。

为验证数据的有效性，我建议将其回放，以便您可以了解数据是否正确。

要验证的更复杂的解决方案是输入测试信号并在示波器或频谱分析仪上查看它。

如何验证Core Audio中的音频幅度是否正确？

1 个答案: