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fixed bw_svf prewarp-related instability bug

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Stefano D'Angelo 2023-05-09 14:31:42 +02:00
parent 2d101a315e
commit 468f66453b
2 changed files with 26 additions and 14 deletions
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2
TODO
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@ -43,7 +43,7 @@ code:
* bw_math: review types
* src inside distortions? w/ control from outside?
* bw_fuzz gain compensation?
* check initial conditions (especially distorsions)
* remove union value = {.f = v};? (std c++ latest)
build system:
* make makefiles handle paths with spaces etc

38
include/bw_svf.h
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@ -20,7 +20,7 @@
/*!
* module_type {{{ dsp }}}
* version {{{ 0.4.0 }}}
* version {{{ 0.5.0 }}}
* requires {{{ bw_config bw_common bw_math bw_one_pole }}}
* description {{{
* State variable filter (2nd order, 12 dB/oct) model with separated lowpass,
@ -28,6 +28,11 @@
* }}}
* changelog {{{
<ul>
* <li>Version <strong>0.5.0</strong>:
* <ul>
* <li>Fixed prewarping-related stability bug.</li>
* </ul>
* </li>
* <li>Version <strong>0.4.0</strong>:
* <ul>
* <li>Added initial input value to
@ -197,8 +202,9 @@ struct _bw_svf_coeffs {
float prewarp_k;
float t;
float kf;
float kbl;
float k;
float kt;
float hp_hb;
float hp_x;
// Parameters
@ -232,24 +238,30 @@ 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) {
const float prewarp_freq = coeffs->prewarp_freq + coeffs->prewarp_k * (coeffs->cutoff - coeffs->prewarp_freq);
float cutoff_cur = bw_one_pole_get_y_z1(&coeffs->smooth_cutoff_state);
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 (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 (cutoff_changed || prewarp_freq_changed || Q_changed) {
if (cutoff_changed || prewarp_freq_changed) {
if (cutoff_changed)
cutoff_cur = bw_one_pole_process1_sticky_rel(&coeffs->smooth_coeffs, &coeffs->smooth_cutoff_state, coeffs->cutoff);
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);
}
coeffs->kbl = coeffs->kf * cutoff_cur;
}
if (Q_changed) {
Q_cur = bw_one_pole_process1_sticky_abs(&coeffs->smooth_coeffs, &coeffs->smooth_Q_state, coeffs->Q);
coeffs->k = bw_rcpf_2(Q_cur);
}
coeffs->kt = coeffs->k + coeffs->t;
coeffs->hp_x = bw_rcpf_2(1.f + coeffs->t * coeffs->kt);
coeffs->hp_hb = coeffs->k + coeffs->kbl;
coeffs->hp_x = bw_rcpf_2(1.f + coeffs->kbl * coeffs->hp_hb);
}
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) {
@ -278,9 +290,9 @@ static inline void bw_svf_process1(const bw_svf_coeffs *BW_RESTRICT coeffs, bw_s
const float kk = coeffs->kf * state->cutoff_z1;
const float lp_xz1 = state->lp_z1 - kk * state->bp_z1;
const float bp_xz1 = state->bp_z1 - kk * state->hp_z1;
*y_hp = coeffs->hp_x * (x + coeffs->kt * bp_xz1 - lp_xz1);
*y_bp = bp_xz1 - coeffs->t * *y_hp;
*y_lp = lp_xz1 - coeffs->t * *y_bp;
*y_hp = coeffs->hp_x * (x + coeffs->hp_hb * bp_xz1 - lp_xz1);
*y_bp = bp_xz1 - coeffs->kbl * *y_hp;
*y_lp = lp_xz1 - coeffs->kbl * *y_bp;
state->hp_z1 = *y_hp;
state->lp_z1 = *y_lp;
state->bp_z1 = *y_bp;