@audio/filter-diode-ladder

Diode ladder filter (Roland TB-303 / EMS VCS3 style)

npm install @audio/filter-diode-ladder

import diodeLadder from '@audio/filter-diode-ladder'

Roland TB-303 / EMS VCS3 style — per-stage saturation gives the characteristic acid "squelch".

Circuit: Roland TB-303, EMS VCS3, EDP Wasp Key difference from Moog: stages are bidirectionally coupled — no unity-gain buffers between them (unlike Moog), so each stage loads its neighbors; solved as one tridiagonal system per sample (Thomas algorithm) instead of Moog's simple forward cascade Character: preserves more bass at high resonance than Moog — closed-form DC gain $1/(1 + 4\cdot\text{resonance})$ vs Moog's $1/(1 + 4\cdot\text{resonance}\cdot(1+G+G^2+G^3+G^4))$, $G<1$ — and more "squelchy"/aggressive due to the per-stage $\tanh$ Implementation: ZDF (zero-delay feedback) via trapezoidal integration — Zavalishin, The Art of VA Filter Design (2012); Pirkle, Designing Audio Effect Plugins in C++, 2nd ed. (2019), Ch. 10 Stability: bounded (per-stage $\tanh$-saturated) across the documented 0–1 range and well beyond; self-oscillates near resonance≈1.15–1.2 — higher than Moog's exact 1, since the extra per-stage $\tanh$ adds damping

let params = { fc: 500, resonance: 0.8, fs: 44100 }
diodeLadder(buffer, params)

| Param | Default | | |---|---|---| | fc | 1000 | cutoff frequency, Hz | | resonance | 0 | 0–1; feedback k = 4·resonance (same mapping as moogLadder); self-oscillates near ≈1.15–1.2 | | fs | 44100 | sample rate, Hz | | drive | 1 | input gain into each stage's tanh saturation; 0 mutes the signal |

Pass the same params object on every call to persist the 4 stage states across blocks.

Use when: acid basslines, squelchy synth leads — resonance character that stays bounded (not self-oscillating) across most of the range, unlike moogLadder.

Part of @audio/filter — the filter family umbrella. This README is generated from the umbrella docs.

MIT © audiojs