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iir_int: rounding bias

This commit is contained in:
Robert Jördens 2021-02-09 12:17:48 +01:00
parent 611bd3e855
commit 31781a9d0e
1 changed files with 4 additions and 4 deletions
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8
dsp/src/iir_int.rs
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@ -28,9 +28,9 @@ impl Vec5 {
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 f64;
let b0 = (k / 2. * (1. - fcos) / a0) as _; let b0 = (k / 2. * (1. - fcos) / a0 + 0.5) as _;
let a1 = (2. * fcos / a0) as _; let a1 = (2. * fcos / a0 + 0.5) as _;
let a2 = ((alpha - 1.) / a0) as _; let a2 = ((alpha - 1.) / a0 + 0.5) as _;
Self([b0, 2 * b0, b0, a1, a2]) Self([b0, 2 * b0, b0, a1, a2])
} }
@ -97,7 +97,7 @@ mod test {
#[test] #[test]
fn lowpass_gen() { fn lowpass_gen() {
let ba = Vec5::lowpass(1e-5, 1. / 2f64.sqrt(), 2e5); let ba = Vec5::lowpass(1e-5, 1. / 2f64.sqrt(), 2.);
println!("{:?}", ba.0); println!("{:?}", ba.0);
} }
} }