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iir: tweak math a bit

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This commit is contained in:
Robert Jördens 2021-02-02 15:41:47 +01:00
parent ddbfa9d988
commit dcc71d5d11
1 changed files with 3 additions and 2 deletions
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5
dsp/src/iir_int.rs
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@ -22,8 +22,9 @@ impl Vec5 {
pub fn lowpass(f: f32, q: f32, k: f32) -> Self { pub fn lowpass(f: f32, q: f32, k: f32) -> Self {
// 3rd order Taylor approximation of sin and cos. // 3rd order Taylor approximation of sin and cos.
let f = f * 2. * PI; let f = f * 2. * PI;
let fsin = f - f * f * f / 6.; let f2 = f * f * 0.5;
let fcos = 1. - f * f / 2.; let fcos = 1. - f2;
let fsin = f * (1. - f2 / 3.);
let alpha = fsin / (2. * q); let alpha = fsin / (2. * q);
// IIR uses Q2.30 fixed point // IIR uses Q2.30 fixed point
let a0 = (1. + alpha) / (1 << IIR::SHIFT) as f32; let a0 = (1. + alpha) / (1 << IIR::SHIFT) as f32;