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adjusted the Simper SVF to use the sin() coefficient calculation.

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This commit is contained in:
Weird Constructor 2021-07-19 18:46:45 +02:00
parent 888205b3ef
commit 52649a9875
1 changed files with 20 additions and 12 deletions
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32
src/dsp/helpers.rs
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@ -1011,27 +1011,35 @@ pub fn process_hal_chamberlin_svf(
/// // ... do something with the result here.
/// }
///```
// Simper SVF taken from baseplug (Rust crate) example svf_simper.rs:
// implemented from https://cytomic.com/files/dsp/SvfLinearTrapOptimised2.pdf
// thanks, andy!
// Simper SVF implemented from
// https://cytomic.com/files/dsp/SvfLinearTrapezoidalSin.pdf
// Big thanks go to Andrew Simper @ Cytomic for developing and publishing
// the paper.
#[inline]
pub fn process_simper_svf(
input: f32, freq: f32, res: f32, israte: f32, ic1eq: &mut f32, ic2eq: &mut f32
) -> (f32, f32, f32) {
let g = (std::f32::consts::PI * freq * israte).tan();
// XXX: the 1.989 were tuned by hand, so the resonance is more audible.
let k = 2f32 - (1.989f32 * res);
let w = std::f32::consts::PI * freq * israte;
let a1 = 1.0 / (1.0 + (g * (g + k)));
let a2 = g * a1;
let a3 = g * a2;
let s1 = w.sin();
let s2 = (2.0 * w).sin();
let nrm = 1.0 / (2.0 + k * s2);
let v3 = input - *ic2eq;
let v1 = (a1 * *ic1eq) + (a2 * v3);
let v2 = *ic2eq + (a2 * *ic1eq) + (a3 * v3);
let g0 = s2 * nrm;
let g1 = (-2.0 * s1 * s1 - k * s2) * nrm;
let g2 = (2.0 * s1 * s1) * nrm;
*ic1eq = (2.0 * v1) - *ic1eq;
*ic2eq = (2.0 * v2) - *ic2eq;
let t0 = input - *ic2eq;
let t1 = g0 * t0 + g1 * *ic1eq;
let t2 = g2 * t0 + g0 * *ic1eq;
let v1 = t1 + *ic1eq;
let v2 = t2 + *ic2eq;
*ic1eq += 2.0 * t1;
*ic2eq += 2.0 * t2;
// low = v2
// band = v1