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add custom prewarping option to bw_svf

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This commit is contained in:
Stefano D'Angelo 2023-01-12 20:18:57 +01:00
parent 233a016ba4
commit 97492ce701
2 changed files with 43 additions and 7 deletions
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1
TODO
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@ -21,6 +21,7 @@ code:
* should rather use backward Euler in bw_onepole?
* Q to slope and viceversa functions in 2nd order shelf filters? keep updated values (seamless switch, syncrhonicity)?
* treat unused variable/function warnings
* csch for bw_peak bandwidth -> Q
build system:
* make makefiles handle paths with spaces etc

49
include/bw_svf.h
View File

@ -137,6 +137,25 @@ static inline void bw_svf_set_Q(bw_svf_coeffs *BW_RESTRICT coeffs, float value);
* `value` must be equal or bigger than `0.5f`.
*
* Default value: `0.5f`.
*
* #### bw_svf_set_prewarp_at_cutoff()
* ```>>> */
static inline void bw_svf_set_prewarp_at_cutoff(bw_svf_coeffs *BW_RESTRICT coeffs, char value);
/*! <<<```
* Sets whether bilinear transform prewarping frequency should match the
* cutoff frequency (non-`0`) or not (`0`).
*
* Default value: non-`0` (on).
*
* #### bw_svf_set_prewarp_freq()
* ```>>> */
static inline void bw_svf_set_prewarp_freq(bw_svf_coeffs *BW_RESTRICT coeffs, float value);
/*! <<<```
* Sets the prewarping frequency `value` (Hz) in `coeffs`.
*
* Only used when the prewarp\_at\_cutoff parameter is off.
*
* Default value: `1e3f`.
* }}} */
/*** Implementation ***/
@ -152,10 +171,12 @@ struct _bw_svf_coeffs {
bw_one_pole_coeffs smooth_coeffs;
bw_one_pole_state smooth_cutoff_state;
bw_one_pole_state smooth_Q_state;
bw_one_pole_state smooth_prewarp_freq_state;
// Coefficients
float t_k;
float prewarp_k;
float t;
float kf;
float k;
@ -165,6 +186,7 @@ struct _bw_svf_coeffs {
// Parameters
float cutoff;
float Q;
float prewarp_freq;
};
struct _bw_svf_state {
@ -180,6 +202,8 @@ static inline void bw_svf_init(bw_svf_coeffs *BW_RESTRICT coeffs) {
bw_one_pole_set_sticky_thresh(&coeffs->smooth_coeffs, 1e-3f);
coeffs->cutoff = 1e3f;
coeffs->Q = 0.5f;
coeffs->prewarp_freq = 1e3f;
coeffs->prewarp_k = 1.f;
}
static inline void bw_svf_set_sample_rate(bw_svf_coeffs *BW_RESTRICT coeffs, float sample_rate) {
@ -189,15 +213,16 @@ static inline void bw_svf_set_sample_rate(bw_svf_coeffs *BW_RESTRICT coeffs, flo
}
static inline void _bw_svf_do_update_coeffs(bw_svf_coeffs *BW_RESTRICT coeffs, char force) {
float cutoff_cur = bw_one_pole_get_y_z1(&coeffs->smooth_cutoff_state);
const float prewarp_freq = coeffs->prewarp_freq + coeffs->prewarp_k * (coeffs->cutoff - coeffs->prewarp_freq);
float prewarp_freq_cur = bw_one_pole_get_y_z1(&coeffs->smooth_prewarp_freq_state);
float Q_cur = bw_one_pole_get_y_z1(&coeffs->smooth_Q_state);
const char cutoff_changed = force || coeffs->cutoff != cutoff_cur;
const char prewarp_freq_changed = force || prewarp_freq != prewarp_freq_cur;
const char Q_changed = force || coeffs->Q != Q_cur;
if (cutoff_changed || Q_changed) {
if (cutoff_changed) {
cutoff_cur = bw_one_pole_process1_sticky_rel(&coeffs->smooth_coeffs, &coeffs->smooth_cutoff_state, coeffs->cutoff);
coeffs->t = bw_tanf_3(coeffs->t_k * cutoff_cur);
coeffs->kf = coeffs->t * bw_rcpf_2(cutoff_cur);
if (prewarp_freq_changed || Q_changed) {
if (prewarp_freq_changed) {
prewarp_freq_cur = bw_one_pole_process1_sticky_rel(&coeffs->smooth_coeffs, &coeffs->smooth_prewarp_freq_state, prewarp_freq);
coeffs->t = bw_tanf_3(coeffs->t_k * prewarp_freq_cur);
coeffs->kf = coeffs->t * bw_rcpf_2(prewarp_freq_cur);
}
if (Q_changed) {
Q_cur = bw_one_pole_process1_sticky_abs(&coeffs->smooth_coeffs, &coeffs->smooth_Q_state, coeffs->Q);
@ -206,11 +231,13 @@ static inline void _bw_svf_do_update_coeffs(bw_svf_coeffs *BW_RESTRICT coeffs, c
coeffs->kt = coeffs->k + coeffs->t;
coeffs->hp_x = bw_rcpf_2(1.f + coeffs->t * coeffs->kt);
}
bw_one_pole_process1(&coeffs->smooth_coeffs, &coeffs->smooth_cutoff_state, coeffs->cutoff);
}
static inline void bw_svf_reset_coeffs(bw_svf_coeffs *BW_RESTRICT coeffs) {
bw_one_pole_reset_state(&coeffs->smooth_coeffs, &coeffs->smooth_cutoff_state, coeffs->cutoff);
bw_one_pole_reset_state(&coeffs->smooth_coeffs, &coeffs->smooth_Q_state, coeffs->Q);
bw_one_pole_reset_state(&coeffs->smooth_coeffs, &coeffs->smooth_prewarp_freq_state, coeffs->prewarp_freq + coeffs->prewarp_k * (coeffs->cutoff - coeffs->prewarp_freq));
_bw_svf_do_update_coeffs(coeffs, 1);
}
@ -312,6 +339,14 @@ static inline void bw_svf_set_Q(bw_svf_coeffs *BW_RESTRICT coeffs, float value)
coeffs->Q = value;
}
static inline void bw_svf_set_prewarp_at_cutoff(bw_svf_coeffs *BW_RESTRICT coeffs, char value) {
coeffs->prewarp_k = value ? 1.f : 0.f;
}
static inline void bw_svf_set_prewarp_freq(bw_svf_coeffs *BW_RESTRICT coeffs, float value) {
coeffs->prewarp_freq = value;
}
#ifdef __cplusplus
}
#endif