From 52649a9875b1a214d2f7cd575dae4cc636b8ab07 Mon Sep 17 00:00:00 2001 From: Weird Constructor Date: Mon, 19 Jul 2021 18:46:45 +0200 Subject: [PATCH] adjusted the Simper SVF to use the sin() coefficient calculation. --- src/dsp/helpers.rs | 32 ++++++++++++++++++++------------ 1 file changed, 20 insertions(+), 12 deletions(-) diff --git a/src/dsp/helpers.rs b/src/dsp/helpers.rs index 884744d..21311e3 100644 --- a/src/dsp/helpers.rs +++ b/src/dsp/helpers.rs @@ -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