DarkLumi

DarkLumi — Opto Bus Compressor

A schematic-accurate Vactrol-based opto bus compressor — feedback topology, Class-A solid-state audio path, dual-cell envelope, and 17 modeled output transformers. Where DarkComp gives you the LA-2A style hybrid for mix bus duty, DarkLumi is the dedicated opto-on-the-bus tool: bigger, smoother, more “leaning” than VCA bus comps, with the natural soft knee that only a real photocell can deliver.

Topology:

• Vactrol VTL5C3-style photocell — natural I-V curve produces an inherently soft knee with no formula required
• Class-A solid-state audio path — fast op-amps with +20 dBu headroom for clean, modern bus duty (no tube coloration)
• Feedback topology — sidechain taps post-opto, post-output op-amp (the LA-2A / CL1B / Tube-Tech architecture)
• Dual-cell envelope — fast cell handles transients (~5–15 ms), slow cell handles sustain (~150 ms–2.5 s), with program-dependent crossfade modeling the classic opto “memory” effect (hard compression takes longer to recover than light compression)
• H2-dominant harmonic signature — the warm/round tone of opto bus comps vs the H3-dominant VCA character
• London-mode summed mono sidechain detection (prevOutL + prevOutR) / 2
• Stable feedback path — prevOutL/prevOutR persisted across processBlock boundaries, envelope clamped for guaranteed stability

Controls:

• Threshold: continuous -100 to 0 dB
• Ratio: 7-stop ladder — 2:1, 2.5:1, 4:1, 6:1, 8:1, 10:1, 20:1
• Attack: continuous 0.1–30 ms (log-skewed, centered at 3 ms) — tilts the photocell baseline rather than overriding it
• Release: continuous 0.05–1.5 s with Auto Release (dual-time-constant program-dependent)
• Mix: 0–100% parallel compression
• Knee: -10 to +10 offset (hard knee to mastering-soft)

Pro Extras:

• 6-band Output EQ — full parametric (Bell / LShelf / HShelf / LCut / HCut), post-compression
• 17-mode Output Transformer: None / Carnhill / Sowter / Cinemag / Marinair / Haufe V72 / Triad HS-30 / Reichenbach / EA Edcor / Neve 1272 / API 2520 / UTC A-20 / Peerless S-415 / St Ives / Lundahl LL1538 / Jensen JT-11 / Tamura TKS-27
• Input Gain with auto-compensation FB/FF Feedback/FeedForward
• Saturation — drives the Class-A op-amp stage with auto-compensated output (hear character, not volume)
• Output Gain (±12 dB final trim)
• x2 / x4 / x8 oversampling
• Phase-aligned dry buffer for parallel compression
• Host bypass with sample-aligned PDC compensation