问题
The title explains my problem.
What I am trying to do is quite simple:
- Load MP3 track (via libmpg123)
- Read samples
- Apply Kiss FFT on the samples
What I have tried so far
inline float scale(kiss_fft_scalar val)
{
int g = 0;
return val < 0 ? val*(1/32768.0f ) : val*(1/32767.0f);
}
void main()
{
mpg123_handle *m = NULL;
int channels = 0, encoding = 0;
long rate = 0;
int err = MPG123_OK;
err = mpg123_init();
m = mpg123_new(NULL, &err);
mpg123_open(m, "L:\\audio-io\\audio-analysis\\samples\\zero.mp3");
mpg123_getformat(m, &rate, &channels, &encoding);
err = mpg123_format_none(m);
err = mpg123_format(m, rate, channels, encoding);
// Get 2048 samples
const int TIME = 2048;
// 16-bit integer encoded in bytes, hence x2 size
unsigned char* buffer = new unsigned char[TIME*2];
size_t done = 0;
err = mpg123_read(m, buffer, TIME*2, &done);
short* samples = new short[done/2];
int index = 0;
// Iterate 2 bytes at a time
for (int i = 0; i < done; i += 2)
{
unsigned char first = buffer[i];
unsigned char second = buffer[i + 1];
samples[index++] = (first | (second << 8));
}
// Array to store the calculated data
int speclen = TIME / 2 + 1;
float* output = new float[speclen];
kiss_fftr_cfg config;
kiss_fft_cpx* spectrum;
config = kiss_fftr_alloc(TIME, 0, NULL, NULL);
spectrum = (kiss_fft_cpx*) malloc(sizeof(kiss_fft_cpx) * TIME);
// Right here...
kiss_fftr(config, (kiss_fft_scalar*) samples, spectrum);
for (int i = 0; i < speclen; i++)
{
float re = scale(spectrum[i].r) * TIME;
float im = scale(spectrum[i].i) * TIME;
output[i] = sqrtf(re*re + im*im);
}
return;
}
The problem occurs at this line kiss_fftr(config, (kiss_fft_scalar*) samples, spectrum);
Where samples contains the audio samples (16 bit), and spectrum is suppose to hold the output data.
After the function completes, here is what's happening in the debugger window.
Can someone give me a simple example of how to apply Kiss FFT functions on audio (16 bit encoded) samples?
回答1:
You need to find the bug(s) in your code. My test code appears to work just fine.
Complex-valued forward FFT with floats:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "kiss_fft.h"
#ifndef M_PI
#define M_PI 3.14159265358979324
#endif
#define N 16
void TestFft(const char* title, const kiss_fft_cpx in[N], kiss_fft_cpx out[N])
{
kiss_fft_cfg cfg;
printf("%s\n", title);
if ((cfg = kiss_fft_alloc(N, 0/*is_inverse_fft*/, NULL, NULL)) != NULL)
{
size_t i;
kiss_fft(cfg, in, out);
free(cfg);
for (i = 0; i < N; i++)
printf(" in[%2zu] = %+f , %+f "
"out[%2zu] = %+f , %+f\n",
i, in[i].r, in[i].i,
i, out[i].r, out[i].i);
}
else
{
printf("not enough memory?\n");
exit(-1);
}
}
int main(void)
{
kiss_fft_cpx in[N], out[N];
size_t i;
for (i = 0; i < N; i++)
in[i].r = in[i].i = 0;
TestFft("Zeroes (complex)", in, out);
for (i = 0; i < N; i++)
in[i].r = 1, in[i].i = 0;
TestFft("Ones (complex)", in, out);
for (i = 0; i < N; i++)
in[i].r = sin(2 * M_PI * 4 * i / N), in[i].i = 0;
TestFft("SineWave (complex)", in, out);
return 0;
}
Output:
Zeroes (complex)
in[ 0] = +0.000000 , +0.000000 out[ 0] = +0.000000 , +0.000000
in[ 1] = +0.000000 , +0.000000 out[ 1] = +0.000000 , +0.000000
in[ 2] = +0.000000 , +0.000000 out[ 2] = +0.000000 , +0.000000
in[ 3] = +0.000000 , +0.000000 out[ 3] = +0.000000 , +0.000000
in[ 4] = +0.000000 , +0.000000 out[ 4] = +0.000000 , +0.000000
in[ 5] = +0.000000 , +0.000000 out[ 5] = +0.000000 , +0.000000
in[ 6] = +0.000000 , +0.000000 out[ 6] = +0.000000 , +0.000000
in[ 7] = +0.000000 , +0.000000 out[ 7] = +0.000000 , +0.000000
in[ 8] = +0.000000 , +0.000000 out[ 8] = +0.000000 , +0.000000
in[ 9] = +0.000000 , +0.000000 out[ 9] = +0.000000 , +0.000000
in[10] = +0.000000 , +0.000000 out[10] = +0.000000 , +0.000000
in[11] = +0.000000 , +0.000000 out[11] = +0.000000 , +0.000000
in[12] = +0.000000 , +0.000000 out[12] = +0.000000 , +0.000000
in[13] = +0.000000 , +0.000000 out[13] = +0.000000 , +0.000000
in[14] = +0.000000 , +0.000000 out[14] = +0.000000 , +0.000000
in[15] = +0.000000 , +0.000000 out[15] = +0.000000 , +0.000000
Ones (complex)
in[ 0] = +1.000000 , +0.000000 out[ 0] = +16.000000 , +0.000000
in[ 1] = +1.000000 , +0.000000 out[ 1] = +0.000000 , +0.000000
in[ 2] = +1.000000 , +0.000000 out[ 2] = +0.000000 , +0.000000
in[ 3] = +1.000000 , +0.000000 out[ 3] = +0.000000 , +0.000000
in[ 4] = +1.000000 , +0.000000 out[ 4] = +0.000000 , +0.000000
in[ 5] = +1.000000 , +0.000000 out[ 5] = +0.000000 , +0.000000
in[ 6] = +1.000000 , +0.000000 out[ 6] = +0.000000 , +0.000000
in[ 7] = +1.000000 , +0.000000 out[ 7] = +0.000000 , +0.000000
in[ 8] = +1.000000 , +0.000000 out[ 8] = +0.000000 , +0.000000
in[ 9] = +1.000000 , +0.000000 out[ 9] = +0.000000 , +0.000000
in[10] = +1.000000 , +0.000000 out[10] = +0.000000 , +0.000000
in[11] = +1.000000 , +0.000000 out[11] = +0.000000 , +0.000000
in[12] = +1.000000 , +0.000000 out[12] = +0.000000 , +0.000000
in[13] = +1.000000 , +0.000000 out[13] = +0.000000 , +0.000000
in[14] = +1.000000 , +0.000000 out[14] = +0.000000 , +0.000000
in[15] = +1.000000 , +0.000000 out[15] = +0.000000 , +0.000000
SineWave (complex)
in[ 0] = +0.000000 , +0.000000 out[ 0] = +0.000000 , +0.000000
in[ 1] = +1.000000 , +0.000000 out[ 1] = +0.000000 , +0.000000
in[ 2] = +0.000000 , +0.000000 out[ 2] = +0.000000 , +0.000000
in[ 3] = -1.000000 , +0.000000 out[ 3] = +0.000000 , +0.000000
in[ 4] = +0.000000 , +0.000000 out[ 4] = +0.000000 , -8.000000
in[ 5] = +1.000000 , +0.000000 out[ 5] = +0.000000 , +0.000000
in[ 6] = +0.000000 , +0.000000 out[ 6] = +0.000000 , +0.000000
in[ 7] = -1.000000 , +0.000000 out[ 7] = +0.000000 , +0.000000
in[ 8] = +0.000000 , +0.000000 out[ 8] = +0.000000 , +0.000000
in[ 9] = +1.000000 , +0.000000 out[ 9] = +0.000000 , +0.000000
in[10] = +0.000000 , +0.000000 out[10] = +0.000000 , +0.000000
in[11] = -1.000000 , +0.000000 out[11] = +0.000000 , +0.000000
in[12] = +0.000000 , +0.000000 out[12] = +0.000000 , +8.000000
in[13] = +1.000000 , +0.000000 out[13] = +0.000000 , +0.000000
in[14] = +0.000000 , +0.000000 out[14] = +0.000000 , +0.000000
in[15] = -1.000000 , +0.000000 out[15] = +0.000000 , +0.000000
Real-valued forward FFT with floats:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "kiss_fftr.h"
#ifndef M_PI
#define M_PI 3.14159265358979324
#endif
#define N 16
void TestFftReal(const char* title, const kiss_fft_scalar in[N], kiss_fft_cpx out[N / 2 + 1])
{
kiss_fftr_cfg cfg;
printf("%s\n", title);
if ((cfg = kiss_fftr_alloc(N, 0/*is_inverse_fft*/, NULL, NULL)) != NULL)
{
size_t i;
kiss_fftr(cfg, in, out);
free(cfg);
for (i = 0; i < N; i++)
{
printf(" in[%2zu] = %+f ",
i, in[i]);
if (i < N / 2 + 1)
printf("out[%2zu] = %+f , %+f",
i, out[i].r, out[i].i);
printf("\n");
}
}
else
{
printf("not enough memory?\n");
exit(-1);
}
}
int main(void)
{
kiss_fft_scalar in[N];
kiss_fft_cpx out[N / 2 + 1];
size_t i;
for (i = 0; i < N; i++)
in[i] = 0;
TestFftReal("Zeroes (real)", in, out);
for (i = 0; i < N; i++)
in[i] = 1;
TestFftReal("Ones (real)", in, out);
for (i = 0; i < N; i++)
in[i] = sin(2 * M_PI * 4 * i / N);
TestFftReal("SineWave (real)", in, out);
return 0;
}
Output:
Zeroes (real)
in[ 0] = +0.000000 out[ 0] = +0.000000 , +0.000000
in[ 1] = +0.000000 out[ 1] = +0.000000 , +0.000000
in[ 2] = +0.000000 out[ 2] = +0.000000 , +0.000000
in[ 3] = +0.000000 out[ 3] = +0.000000 , +0.000000
in[ 4] = +0.000000 out[ 4] = +0.000000 , +0.000000
in[ 5] = +0.000000 out[ 5] = +0.000000 , +0.000000
in[ 6] = +0.000000 out[ 6] = +0.000000 , +0.000000
in[ 7] = +0.000000 out[ 7] = +0.000000 , +0.000000
in[ 8] = +0.000000 out[ 8] = +0.000000 , +0.000000
in[ 9] = +0.000000
in[10] = +0.000000
in[11] = +0.000000
in[12] = +0.000000
in[13] = +0.000000
in[14] = +0.000000
in[15] = +0.000000
Ones (real)
in[ 0] = +1.000000 out[ 0] = +16.000000 , +0.000000
in[ 1] = +1.000000 out[ 1] = +0.000000 , +0.000000
in[ 2] = +1.000000 out[ 2] = +0.000000 , +0.000000
in[ 3] = +1.000000 out[ 3] = +0.000000 , +0.000000
in[ 4] = +1.000000 out[ 4] = +0.000000 , +0.000000
in[ 5] = +1.000000 out[ 5] = +0.000000 , +0.000000
in[ 6] = +1.000000 out[ 6] = +0.000000 , +0.000000
in[ 7] = +1.000000 out[ 7] = +0.000000 , +0.000000
in[ 8] = +1.000000 out[ 8] = +0.000000 , +0.000000
in[ 9] = +1.000000
in[10] = +1.000000
in[11] = +1.000000
in[12] = +1.000000
in[13] = +1.000000
in[14] = +1.000000
in[15] = +1.000000
SineWave (real)
in[ 0] = +0.000000 out[ 0] = +0.000000 , +0.000000
in[ 1] = +1.000000 out[ 1] = +0.000000 , +0.000000
in[ 2] = +0.000000 out[ 2] = +0.000000 , +0.000000
in[ 3] = -1.000000 out[ 3] = +0.000000 , +0.000000
in[ 4] = +0.000000 out[ 4] = +0.000000 , -8.000000
in[ 5] = +1.000000 out[ 5] = +0.000000 , +0.000000
in[ 6] = +0.000000 out[ 6] = +0.000000 , +0.000000
in[ 7] = -1.000000 out[ 7] = +0.000000 , +0.000000
in[ 8] = +0.000000 out[ 8] = +0.000000 , +0.000000
in[ 9] = +1.000000
in[10] = +0.000000
in[11] = -1.000000
in[12] = +0.000000
in[13] = +1.000000
in[14] = +0.000000
in[15] = -1.000000
回答2:
When I first started looking at this answer I kept wondering why the -8.0 was turning up in the imaginary component rather than the real part. It was whilst re-reading a printed article on FFT's that I realised I'd been thinking about magnitude.
So I tweaked the answer in the Complex code to change the printf as follows
for (i = 0; i < N; i++)
printf(" in[%02i]=%+f, %+f out[%02i]=%+f, %+f M[%02i]=%+f\n",
i, in[i].r, in[i].i,
i, out[i].r, out[i].i,
i, sqrt((out[i].r * out[i].r) + (out[i].i * out[i].i)));
Which produces an answer showing the magnitude as well.
...
SineWave (complex)
in[00]=+0.000000, +0.000000 out[00]=+0.000000, +0.000000 M[00]=+0.000000
in[01]=+1.000000, +0.000000 out[01]=+0.000000, +0.000000 M[01]=+0.000000
in[02]=+0.000000, +0.000000 out[02]=+0.000000, +0.000000 M[02]=+0.000000
in[03]=-1.000000, +0.000000 out[03]=+0.000000, +0.000000 M[03]=+0.000000
in[04]=-0.000000, +0.000000 out[04]=-0.000000, -8.000000 M[04]=+8.000000
in[05]=+1.000000, +0.000000 out[05]=+0.000000, -0.000000 M[05]=+0.000000
in[06]=+0.000000, +0.000000 out[06]=+0.000000, -0.000000 M[06]=+0.000000
in[07]=-1.000000, +0.000000 out[07]=+0.000000, -0.000000 M[07]=+0.000000
in[08]=-0.000000, +0.000000 out[08]=+0.000000, +0.000000 M[08]=+0.000000
in[09]=+1.000000, +0.000000 out[09]=+0.000000, +0.000000 M[09]=+0.000000
in[10]=+0.000000, +0.000000 out[10]=+0.000000, +0.000000 M[10]=+0.000000
in[11]=-1.000000, +0.000000 out[11]=+0.000000, +0.000000 M[11]=+0.000000
in[12]=-0.000000, +0.000000 out[12]=-0.000000, +8.000000 M[12]=+8.000000
in[13]=+1.000000, +0.000000 out[13]=+0.000000, -0.000000 M[13]=+0.000000
in[14]=+0.000000, +0.000000 out[14]=+0.000000, -0.000000 M[14]=+0.000000
in[15]=-1.000000, +0.000000 out[15]=+0.000000, -0.000000 M[15]=+0.000000
I also played around changing the frequency in the for loop that generates the sine wave.
float freq;
...
freq = 6.0;
for (i = 0; i < N; i++)
in[i].r = sin(2 * M_PI * freq * i / N), in[i].i = 0;
And so long as I stayed with multiples of 1.0 and under the Nyquist frequency 16/2 = 8 the result shifted from bin to bin quite nicely. Of course setting the frequency to fractional values sees its magnitude spread across the bins and without applying a windowing function we get leakage. If you are still struggling with FFT's like I am play around with code like this where you can see all of the results on a single screen for a while and things start to become clearer.
Finally a vote of thanks to Alexey for the answer it helped me get started with Kiss FFT.
回答3:
Try this:
in[i].r = sin(2 * M_PI * freq * (i / N*1.00)), in[i].i = 0;
来源：https://stackoverflow.com/questions/14536950/applying-kiss-fft-on-audio-samples-and-getting-nan-output