Phase 1 — IEC 61260 Butterworth 1/n‑Octave Filter Designer (ΔA, no ∞ tails)

Bandwidth (1/n)

Center (exact) fm [Hz]

Fs [Hz]

Total band‑pass order

IEC Class

ΔA axis range [dB]

Filter = HP(f₁) × LP(f₂) via pre‑warped bilinear transform; orders split ⌊M/2⌋ (HP) and ⌈M/2⌉ (LP). Cascade gain normalized at fm.
Plot is in ΔA space (IEC 61260‑1 §4.4): ΔA(f) = −|H(f)| (dB) with |H(fm)| ≈ 0 dB. IEC minimum/maximum limits are drawn only where defined; +∞ regions are intentionally not drawn.

Summary

SOS (biquad / first‑order) coefficients

Per section: {b:[b0,b1,b2], a:[1,a1,a2]}. First‑order has b2=a2=0.