mirror/sointu
1
0
Fork 0
mirror of https://github.com/vsariola/sointu.git synced 2026-02-02 05:40:15 -05:00
Code Issues Packages Projects Releases Wiki Activity

drafting

Browse Source
This commit is contained in:
5684185+vsariola@users.noreply.github.com
2026-01-17 17:23:46 +02:00
parent 655d736149
commit fd5e2c3bb8
1 changed files with 13 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
tracker/spectrum.go
View File

@ -77,22 +77,27 @@ func (m *Model) BiquadCoeffs() (coeffs BiquadCoeffs, ok bool) {
// in state-space, the filter has the form:
// s(n+1) = A*s(n)+B*u, where A = [1 f;-f 1-f*r-f*f] and B = [0;f]
// y(n) = C*s(n)+D*u, where
// C = [low band]
//
// C_low = [1 0]*z, C_band = [0 1]*z, C_high = [-1 -f-r], D_high = [1]
// The transfer function is then H(z) = C*(zI-A)^-1*B + D
// z*I-A = [z-1 -f; f z+f*r+f*f-1]
// Invert it:
// (z*I-A)^-1 = 1/det * [z+f*r+f*f-1 f; -f z-1], where det = (z-1)*(z+f*r+f*f-1)+f^2 = z^2 + z * (f*r+f*f−2) + 1-f*r
// (z*I-A)^-1*B = 1/det * [-f*f; f*z-f]
// (z*I-A)^-1 = 1/det * [z+f*r+f*f-1 f; -f z-1], where det = (z-1)*(z+f*r+f*f-1)+f^2 = z*z+z*f*r+z*f*f-z-z-f*r-f*f+1+f^2 = z*z + z*(f*r+f*f-2)-f*r+1
// (z*I-A)^-1*B = 1/det * f * [f; z-1]
// Low: z * [1,0] * f * [f;z-1] / det = f*f*z / det
// Band: z * [0,1] * f * [f;z-1] / det = (f*z^2-f*z) / det
// High: [-1,-f-r] * f * [f;z-1] / det + 1 = ((-f*f-r*f)*z+r*f)/det + 1 = ((-f*f-r*f)*z+r*f+det)/det = (z^2-2*z+1)/det
var a0 float32 = 1
var a1 float32 = r*f + f*f - 2
var a2 float32 = 1 - r*f
var a2 float32 = 1 - f*r
var b0, b1, b2 float32
if p["lowpass"] == 1 {
b2 = -f * f
b1 = f * f
}
b2 -= f * float32(p["bandpass"])
b1 += f * float32(p["bandpass"])
b0 += f * float32(p["bandpass"])
b1 -= f * float32(p["bandpass"])
b0 += float32(p["highpass"])
b1 += -2 * float32(p["highpass"])
b2 += float32(p["highpass"])
return BiquadCoeffs{a0: a0, a1: a1, a2: a2, b0: b0, b1: b1, b2: b2}, true
case "belleq":
f := float32(m.d.Song.Patch[i].Units[u].Parameters["frequency"]) / 128