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Calculate imaginary part correctly.

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This commit is contained in:
Themaister 2012-02-28 00:29:45 +01:00
parent c975145914
commit c8173aaf62
1 changed files with 12 additions and 6 deletions

18
audio/test/snr.c

@ -112,7 +112,7 @@ static void calculate_fft(const float *data, complex double *butterfly_buf, size
// We only have real data.
for (unsigned i = 1; i < samples / 2; i++)
butterfly_buf[i] += butterfly_buf[samples - i];
butterfly_buf[i] += conj(butterfly_buf[samples - i]);
// Normalize amplitudes.
for (unsigned i = 0; i < samples / 2; i++)
@ -125,23 +125,29 @@ static void test_fft(void)
float signal[32];
complex double butterfly_buf[16];
const float freqs[] = {
const float cos_freqs[] = {
1.0, 4.0, 6.0,
};
const float sin_freqs[] = {
-2.0, 5.0, 7.0,
};
for (unsigned i = 0; i < 16; i++)
{
signal[2 * i] = 0.0;
for (unsigned j = 0; j < sizeof(freqs) / sizeof(freqs[0]); j++)
signal[2 * i] += cos(2.0 * M_PI * i * freqs[j] / 16.0);
for (unsigned j = 0; j < sizeof(cos_freqs) / sizeof(cos_freqs[0]); j++)
signal[2 * i] += cos(2.0 * M_PI * i * cos_freqs[j] / 16.0);
for (unsigned j = 0; j < sizeof(sin_freqs) / sizeof(sin_freqs[0]); j++)
signal[2 * i] += sin(2.0 * M_PI * i * sin_freqs[j] / 16.0);
}
calculate_fft(signal, butterfly_buf, 16);
printf("FFT: { ");
for (unsigned i = 0; i < 7; i++)
printf("%4.2lf, ", cabs(butterfly_buf[i]));
printf("%4.2lf }\n", cabs(butterfly_buf[7]));
printf("(%4.2lf, %4.2lf), ", creal(butterfly_buf[i]), cimag(butterfly_buf[i]));
printf("(%4.2lf, %4.2lf) }\n", creal(butterfly_buf[7]), cimag(butterfly_buf[7]));
}
// This doesn't yet take account for slight phase distortions,