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Filter improvement: LP and HP filters, added test function

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The -3 dB level at cut-off frequency is now maintained for multiple
iterations.
This commit is contained in:
Andreas Eversberg
2017-01-15 11:08:42 +01:00
parent 799b96c801
commit ac0da3f76e
10 changed files with 186 additions and 32 deletions
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37
src/common/filter.c
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@@ -26,14 +26,18 @@
#define PI M_PI
//#define CASCADE
void filter_lowpass_init(filter_lowpass_t *bq, double frequency, int samplerate)
void filter_lowpass_init(filter_t *bq, double frequency, int samplerate, int iterations)
{
double Fc, Q, K, norm;
if (iterations > 64) {
fprintf(stderr, "%s failed: too many iterations, please fix!\n", __func__);
abort();
}
memset(bq, 0, sizeof(*bq));
Q = sqrt(0.5); /* 0.7071... */
bq->iter = iterations;
Q = pow(sqrt(0.5), 1.0 / (double)iterations); /* 0.7071 @ 1 iteration */
Fc = frequency / (double)samplerate;
K = tan(PI * Fc);
norm = 1 / (1 + K / Q + K * K);
@@ -44,18 +48,31 @@ void filter_lowpass_init(filter_lowpass_t *bq, double frequency, int samplerate)
bq->b2 = (1 - K / Q + K * K) * norm;
}
void filter_lowpass_process(filter_lowpass_t *bq, double *samples, int length, int iterations)
void filter_highpass_init(filter_t *bq, double frequency, int samplerate, int iterations)
{
double Fc, Q, K, norm;
memset(bq, 0, sizeof(*bq));
bq->iter = iterations;
Q = pow(sqrt(0.5), 1.0 / (double)iterations); /* 0.7071 @ 1 iteration */
Fc = frequency / (double)samplerate;
K = tan(PI * Fc);
norm = 1 / (1 + K / Q + K * K);
bq->a0 = 1 * norm;
bq->a1 = -2 * bq->a0;
bq->a2 = bq->a0;
bq->b1 = 2 * (K * K - 1) * norm;
bq->b2 = (1 - K / Q + K * K) * norm;
}
void filter_process(filter_t *bq, double *samples, int length)
{
double a0, a1, a2, b1, b2;
double *z1, *z2;
double in, out;
int iterations = bq->iter;
int i, j;
if (iterations > 10) {
fprintf(stderr, "%s failed: too many iterations, please fix!\n", __func__);
abort();
}
/* get states */
a0 = bq->a0;
a1 = bq->a1;