不知道我在做什么错。我从Accelerate框架获得的结果对我来说似乎是不正确的。任何帮助将非常感激!
这是一些将AForge与vDPS进行比较的图表
这是我运行的vDSP代码
fftSetup = vDSP_create_fftsetup( 16, 2);
// Convert the data into a DSPSplitComplex
int samples = spectrumDataSize;
int samplesOver2 = samples/2;
DSPSplitComplex * complexData = new DSPSplitComplex;
float *realpart = (float *)calloc(samplesOver2, sizeof(float));
float *imagpart = (float *)calloc(samplesOver2, sizeof(float));
complexData->realp = realpart;
complexData->imagp = imagpart;
vDSP_ctoz((DSPComplex *)realData, 2, complexData, 1,samplesOver2);
// Calculate the FFT
// ( I'm assuming here you've already called vDSP_create_fftsetup() )
vDSP_fft_zrip(fftSetup, complexData, 1, log2f(samples), FFT_FORWARD);
// Scale the data
//float scale = (float) FFT_SCALE; //scale is 32
vDSP_vsmul(complexData->realp, 1, &scale, complexData->realp, 1,samplesOver2);
vDSP_vsmul(complexData->imagp, 1, &scale, complexData->imagp, 1, samplesOver2);
vDSP_zvabs(complexData, 1, spectrumData, 1, samples);
free(complexData->realp);
free(complexData->imagp);
delete complexData;
// All done!
return spectrumData;
这就是我在AForge中所做的
foreach (float f in floatData)
{
if (i >= this.fft.Length)
break;
this.fft[i++] = new Complex(f * fftSize, 0);
}
AForge.Math.FourierTransform.FFT(this.fft, FourierTransform.Direction.Forward);
最佳答案
在下面的子程序之后
vDSP_ctoz((DSPComplex *)realData, 2, complexData, 1,samplesOver2);
执行时，
complexData具有samplesOver2元素。但是不久之后，您致电vDSP_zvabs(complexData, 1, spectrumData, 1, samples);
希望
complexData具有samples元素，即两倍。这不可能。另外，
realData的布局如何？我问是因为vDSP_ctoz期望其第一个参数以以下形式布置real0, imag0, real1, imag1, ... real(n-1), imag(n-1).
如果您的数据确实是真实的，则
imag0, imag1, ... imag(n-1)应该全部为0。如果不是，则vDSP_ctoz可能不期望这样。 (除非您以某种巧妙的方式打包实际数据，否则将是原来的两倍)。最后，
vDSP_create_fftsetup( 16, 2);可能应该更改为vDSP_create_fftsetup(16, 0);
================================================== =================
我的示例代码附在后记中:
FFTSetup fftSetup = vDSP_create_fftsetup(
16, // vDSP_Length __vDSP_log2n,
kFFTRadix2 // FFTRadix __vDSP_radix
// CAUTION: kFFTRadix2 is an enum that is equal to 0
// kFFTRadix5 is an enum that is equal to 2
// DO NOT USE 2 IF YOU MEAN kFFTRadix2
);
NSAssert(fftSetup != NULL, @"vDSP_create_fftsetup() failed to allocate storage");
int numSamples = 65536; // numSamples must be an integer power of 2; in this case 65536 = 2 ^ 16
float realData[numSamples];
// Prepare the real data with (ahem) fake data, in this case
// the sum of 3 sinusoidal waves representing a C major chord.
// The fake data is rigged to have a sampling frequency of 44100 Hz (as for a CD).
// As always, the Nyquist frequency is just half the sampling frequency, i.e., 22050 Hz.
for (int i = 0; i < numSamples; i++)
{
realData[i] = sin(2 * M_PI * 261.76300048828125 * i / 44100.0) // C4 = 261.626 Hz
+ sin(2 * M_PI * 329.72717285156250 * i / 44100.0) // E4 = 329.628 Hz
+ sin(2 * M_PI * 392.30804443359375 * i / 44100.0); // G4 = 391.995 Hz
}
float splitReal[numSamples / 2];
float splitImag[numSamples / 2];
DSPSplitComplex splitComplex;
splitComplex.realp = splitReal;
splitComplex.imagp = splitImag;
vDSP_ctoz(
(const DSPComplex *)realData, // const DSPComplex __vDSP_C[],
2, // vDSP_Stride __vDSP_strideC, MUST BE A MULTIPLE OF 2
&splitComplex, // DSPSplitComplex *__vDSP_Z,
1, // vDSP_Stride __vDSP_strideZ,
(numSamples / 2) // vDSP_Length __vDSP_size
);
vDSP_fft_zrip(
fftSetup, // FFTSetup __vDSP_setup,
&splitComplex, // DSPSplitComplex *__vDSP_ioData,
1, // vDSP_Stride __vDSP_stride,
(vDSP_Length)lround(log2(numSamples)), // vDSP_Length __vDSP_log2n,
// IMPORTANT: THE PRECEDING ARGUMENT MUST BE LOG_BASE_2 OF THE NUMBER OF floats IN splitComplex
// FOR OUR EXAMPLE, THIS WOULD BE (numSamples / 2) + (numSamples / 2) = numSamples
kFFTDirection_Forward // FFTDirection __vDSP_direction
);
printf("DC component = %f\n", splitComplex.realp[0]);
printf("Nyquist component = %f\n\n", splitComplex.imagp[0]);
// Next, we compute the Power Spectral Density (PSD) from the FFT.
// (The PSD is just the magnitude-squared of the FFT.)
// (We don't bother with scaling as we are only interested in relative values of the PSD.)
float powerSpectralDensity[(numSamples / 2) + 1]; // the "+ 1" is to make room for the Nyquist component
// We move the Nyquist component out of splitComplex.imagp[0] and place it
// at the end of the array powerSpectralDensity, squaring it as we go:
powerSpectralDensity[numSamples / 2] = splitComplex.imagp[0] * splitComplex.imagp[0];
// We can now zero out splitComplex.imagp[0] since the imaginary part of the DC component is, in fact, zero:
splitComplex.imagp[0] = 0.0;
// Finally, we compute the squares of the magnitudes of the elements of the FFT:
vDSP_zvmags(
&splitComplex, // DSPSplitComplex *__vDSP_A,
1, // vDSP_Stride __vDSP_I,
powerSpectralDensity, // float *__vDSP_C,
1, // vDSP_Stride __vDSP_K,
(numSamples / 2) // vDSP_Length __vDSP_N
);
// We print out a table of the PSD as a function of frequency
// Replace the "< 600" in the for-loop below with "<= (numSamples / 2)" if you want
// the entire spectrum up to and including the Nyquist frequency:
printf("Frequency_in_Hz Power_Spectral_Density\n");
for (int i = 0; i < 600; i++)
{
printf("%f, %f\n", (i / (float)(numSamples / 2)) * 22050.0, powerSpectralDensity[i]);
// Recall that the array index i = 0 corresponds to zero frequency
// and that i = (numSamples / 2) corresponds to the Nyquist frequency of 22050 Hz.
// Frequency values intermediate between these two limits are scaled proportionally (linearly).
}
// The output PSD should be zero everywhere except at the three frequencies
// corresponding to the C major triad. It should be something like this:
/***************************************************************************
DC component = -0.000000
Nyquist component = -0.000000
Frequency_in_Hz Power_Spectral_Density
0.000000, 0.000000
0.672913, 0.000000
1.345825, 0.000000
2.018738, 0.000000
2.691650, 0.000000
.
.
.
260.417175, 0.000000
261.090088, 0.000000
261.763000, 4294967296.000000
262.435913, 0.000000
263.108826, 0.000000
.
.
.
328.381348, 0.000000
329.054260, 0.000000
329.727173, 4294967296.000000
330.400085, 0.000000
331.072998, 0.000000
.
.
.
390.962219, 0.000000
391.635132, 0.000000
392.308044, 4294966784.000000
392.980957, 0.000000
393.653870, 0.000000
.
.
.
***************************************************************************/
vDSP_destroy_fftsetup(fftSetup);
关于ios - AForge FFT与加速FFT产生的结果不同，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/11020434/