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iir lowpass: f32 is sufficient

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Robert Jördens 2021-01-26 19:37:05 +01:00
parent 73c98c947a
commit 7c1fa9695a
1 changed files with 4 additions and 4 deletions
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8
dsp/src/iir_int.rs
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@ -1,4 +1,4 @@
use core::f64::consts::PI; use core::f32::consts::PI;
use serde::{Deserialize, Serialize}; use serde::{Deserialize, Serialize};
/// Generic vector for integer IIR filter. /// Generic vector for integer IIR filter.
@ -19,14 +19,14 @@ impl IIRState {
/// ///
/// # Returns /// # Returns
/// 2nd-order IIR filter coefficients in the form [b0,b1,b2,a1,a2]. a0 is set to -1. /// 2nd-order IIR filter coefficients in the form [b0,b1,b2,a1,a2]. a0 is set to -1.
pub fn lowpass(f: f64, q: f64, k: f64) -> IIRState { pub fn lowpass(f: f32, q: f32, k: f32) -> IIRState {
// 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 fsin = f - f * f * f / 6.;
let fcos = 1. - f * f / 2.; let fcos = 1. - f * f / 2.;
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 f64; let a0 = (1. + alpha) / (1 << IIR::SHIFT) as f32;
let b0 = (k / 2. * (1. - fcos) / a0) as _; let b0 = (k / 2. * (1. - fcos) / a0) as _;
let a1 = (2. * fcos / a0) as _; let a1 = (2. * fcos / a0) as _;
let a2 = ((alpha - 1.) / a0) as _; let a2 = ((alpha - 1.) / a0) as _;
@ -96,7 +96,7 @@ mod test {
#[test] #[test]
fn lowpass_gen() { fn lowpass_gen() {
let ba = IIRState::lowpass(1e-3, 1. / 2f64.sqrt(), 2.); let ba = IIRState::lowpass(1e-3, 1. / 2f32.sqrt(), 2.);
println!("{:?}", ba.0); println!("{:?}", ba.0);
} }
} }