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Attempt to measure phase distortion as well.

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This commit is contained in:
Themaister 2012-02-25 21:17:48 +01:00
parent a03c11d7d0
commit a5c47a568e
1 changed files with 38 additions and 11 deletions
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49
audio/test/snr.c
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@ -22,10 +22,8 @@
#include <math.h> #include <math.h>
#include <assert.h> #include <assert.h>
static void gen_signal(float *out, double freq, double sample_rate, double bias_samples, size_t samples) static void gen_signal(float *out, double omega, double bias_samples, size_t samples)
{ {
double omega = 2.0 * M_PI * freq / sample_rate;
for (size_t i = 0; i < samples; i += 2) for (size_t i = 0; i < samples; i += 2)
{ {
out[i + 0] = cos(((i >> 1) + bias_samples) * omega); out[i + 0] = cos(((i >> 1) + bias_samples) * omega);
@ -47,32 +45,61 @@ static double calculate_gain(const float *orig, const float *resamp, size_t samp
return sqrt(resamp_power / orig_power); return sqrt(resamp_power / orig_power);
} }
static double calculate_phase(const float *orig, const float *resamp, double makeup_gain, size_t samples)
{
double max_correlation = 0.0;
for (size_t i = 0; i < samples; i += 2)
max_correlation += orig[i] * orig[i];
double actual_correlation = 0.0;
for (size_t i = 0; i < samples; i += 2)
{
double resampled = makeup_gain * resamp[i];
actual_correlation += resampled * orig[i];
}
double corr = actual_correlation / max_correlation;
if (corr > 1.0)
corr = 1.0;
if (fabs(corr) < 0.0001)
return 0.5 * M_PI;
else
return acos(corr);
}
struct snr_result struct snr_result
{ {
double snr; double snr;
double gain; double gain;
double phase;
}; };
static void calculate_snr(struct snr_result *res, const float *orig, const float *resamp, size_t samples) static void calculate_snr(struct snr_result *res,
double omega,
float *orig, const float *resamp, size_t samples)
{ {
double noise = 0.0; double noise = 0.0;
double signal = 0.0; double signal = 0.0;
gen_signal(orig, omega, 0, samples);
// Account for gain losses at higher frequencies as it's not really noise. // Account for gain losses at higher frequencies as it's not really noise.
double filter_gain = calculate_gain(orig, resamp, samples); double filter_gain = calculate_gain(orig, resamp, samples);
double makeup_gain = 1.0 / filter_gain; double makeup_gain = 1.0 / filter_gain;
for (size_t i = 0; i < samples; i += 2) double phase = calculate_phase(orig, resamp, makeup_gain, samples);
signal += orig[i] * orig[i];
for (size_t i = 0; i < samples; i += 2) for (size_t i = 0; i < samples; i += 2)
{ {
signal += orig[i] * orig[i];
double diff = makeup_gain * resamp[i] - orig[i]; double diff = makeup_gain * resamp[i] - orig[i];
noise += diff * diff; noise += diff * diff;
} }
res->snr = 10 * log10(signal / noise); res->snr = 10 * log10(signal / noise);
res->gain = 20.0 * log10(filter_gain); res->gain = 20.0 * log10(filter_gain);
res->phase = phase;
} }
int main(int argc, char *argv[]) int main(int argc, char *argv[])
@ -149,10 +176,11 @@ int main(int argc, char *argv[])
for (unsigned i = 0; i < sizeof(freq_list) / sizeof(freq_list[0]) && freq_list[i] < 0.5f * in_rate; i++) for (unsigned i = 0; i < sizeof(freq_list) / sizeof(freq_list[0]) && freq_list[i] < 0.5f * in_rate; i++)
{ {
double omega = 2.0 * M_PI * freq_list[i] / in_rate; double omega = 2.0 * M_PI * freq_list[i] / in_rate;
double omega_out = 2.0 * M_PI * freq_list[i] / out_rate;
double sample_offset; double sample_offset;
resampler_preinit(re, omega, &sample_offset); resampler_preinit(re, omega, &sample_offset);
gen_signal(input, freq_list[i], in_rate, sample_offset, samples); gen_signal(input, omega, sample_offset, samples);
struct resampler_data data = { struct resampler_data data = {
.data_in = input, .data_in = input,
@ -164,13 +192,12 @@ int main(int argc, char *argv[])
resampler_process(re, &data); resampler_process(re, &data);
unsigned out_samples = data.output_frames * 2; unsigned out_samples = data.output_frames * 2;
gen_signal(output_expected, freq_list[i], out_rate, 0, out_samples);
struct snr_result res; struct snr_result res;
calculate_snr(&res, output_expected, output, out_samples); calculate_snr(&res, omega_out, output_expected, output, out_samples);
printf("SNR @ %7.1f Hz: %6.2lf dB, Gain: %6.1f dB\n", printf("SNR @ %7.1f Hz: %6.2lf dB, Gain: %6.1lf dB, Phase: %6.4f rad\n",
freq_list[i], res.snr, res.gain); freq_list[i], res.snr, res.gain, res.phase);
//printf("Generated:\n\t"); //printf("Generated:\n\t");
//for (unsigned i = 0; i < 10; i++) //for (unsigned i = 0; i < 10; i++)