问纯正弦FFT更精确的频率

EN

-(void)createFFTWithBufferSize:(float)bufferSize withAudioData:(float*)data {

  // Setup the length
  _log2n = log2f(bufferSize);

  // Calculate the weights array. This is a one-off operation.
  _FFTSetup = vDSP_create_fftsetup(_log2n, FFT_RADIX2);

  // For an FFT, numSamples must be a power of 2, i.e. is always even
  int nOver2 = bufferSize/2;

  // Populate *window with the values for a hamming window function
  float *window = (float *)malloc(sizeof(float)*bufferSize);
  vDSP_hamm_window(window, bufferSize, 0);
  // Window the samples
  vDSP_vmul(data, 1, window, 1, data, 1, bufferSize);
  free(window);

  // Define complex buffer
 _A.realp = (float *) malloc(nOver2*sizeof(float));
 _A.imagp = (float *) malloc(nOver2*sizeof(float));

}

-(void)updateFFTWithBufferSize:(float)bufferSize withAudioData:(float*)data {

  // For an FFT, numSamples must be a power of 2, i.e. is always even
  int nOver2 = bufferSize/2;

  // Pack samples:
  // C(re) -> A[n], C(im) -> A[n+1]
  vDSP_ctoz((COMPLEX*)data, 2, &_A, 1, nOver2);

  // Perform a forward FFT using fftSetup and A
  // Results are returned in A
  vDSP_fft_zrip(_FFTSetup, &_A, 1, _log2n, FFT_FORWARD);

  // Convert COMPLEX_SPLIT A result to magnitudes
  float amp[nOver2];
  float maxMag = 0;

  for(int i=0; i<nOver2; i++) {
    // Calculate the magnitude
    float mag = _A.realp[i]*_A.realp[i]+_A.imagp[i]*_A.imagp[i];
    maxMag = mag > maxMag ? mag : maxMag;
  }
  for(int i=0; i<nOver2; i++) {
    // Calculate the magnitude
    float mag = _A.realp[i]*_A.realp[i]+_A.imagp[i]*_A.imagp[i];
   // Bind the value to be less than 1.0 to fit in the graph
   amp[i] = [EZAudio MAP:mag leftMin:0.0 leftMax:maxMag rightMin:0.0 rightMax:1.0];
 }

for(int i=0; i<nOver2; i++) {
    // Calculate the magnitude
    float mag = _A.realp[i]*_A.realp[i]+_A.imagp[i]*_A.imagp[i];
    if(maxMag < mag) {
        _i_max = i;
    }
    maxMag = mag > maxMag ? mag : maxMag;
}

float frequency = _i_max / bufferSize * 44100;
NSLog(@"FREQUENCY: %f", frequency);