Dark2A

Dark2A — Tube Optical Leveling Amplifier

Overview

Dark2A is a faithful emulation of the legendary LA-2A tube optical leveling amplifier, built from the ground up around the actual C-10953 Issue C schematic. Every stage in the signal path — the T4B photocell, the 12AX7 input tube, the 12BH7 cathode follower, and the UTC output transformer — is modeled with hardware-matched behavior, giving you the slow, musical, program-dependent compression that defined countless classic vocal, bass, and mix-bus recordings. The plugin runs on Kaiser-windowed 96-tap FIR oversampling up to x8 for clean, alias-free tube saturation, with extensive tonal shaping and sidechain control built in for modern mixing workflows.

Compression Engine

At the core sits an authentic T4B opto-cell model with dual-stage program-dependent release: transients release fast, sustained material releases slow, exactly like the original cell’s photoresistor memory. The R30/C6 feedback path (corner ~339Hz) is always-on, intrinsic to the LA-2A sidechain, giving the compression its characteristic frequency-dependent envelope. Peak Reduction drives the amount of compression from gentle leveling to deep limiting, while Gain provides up to 40dB of make-up. Limiter Mode switches the unit into faster, harder limiting behavior matching the original LA-2A’s Compress/Limit toggle. Knee offsets the compression threshold by ±10dB for fine-tuning the onset.

Tube + Transformer Path

The audio path runs through a modeled 12AX7 triode waveshaper into a 12BH7 cathode follower and out through a UTC-style output transformer with low-shelf warmth, HF rolloff, presence lift, and ~180Hz low-mid sag. A subtle heater drift LFO modulates tube bias for organic micro-movement, and transformer hysteresis adds non-linear magnetization behavior. Saturation scales the harmonic content from -100 (clean, harmonics muted) to +100 (doubled harmonics) with 0 representing the default PR-driven response. Input Gain (±18dB) lets you push or back off the tube stage independently of the compression amount.

HF Emphasis (R37)

A switchable sidechain HF emphasis circuit modeling the variable R37 + C12 RC network of the original. Engaged, it makes the compressor more sensitive to high frequencies, ideal for de-essing duties or controlling bright vocals and cymbals without dulling the program signal.

Tonal Section

Four post-compression tone controls let you shape the compressed signal directly: Low (low shelf @ 100Hz, ±12dB), LMID (low-mid shelf @ 250Hz, ±12dB), HMID (bell @ 2kHz, ±12dB), and High (high shelf @ 15kHz, ±12dB). These work on the compressed bus, so EQ moves interact with the compression character — perfect for adding air, weight, or presence after gain reduction.

6-Band Sidechain EQ with Spectrum Analyzer

A full 6-band parametric sidechain EQ shapes what the compressor reacts to without affecting the audio path. Each band offers Bell, Low Shelf, High Shelf, Low Cut, and High Cut types, with frequency (20Hz–20kHz), gain (±18dB), and Q (0.1–18) controls. Default frequencies span 80Hz, 250Hz, 800Hz, 2.5kHz, 6kHz, and 12kHz. A built-in 2048-point FFT spectrum analyzer visualizes the sidechain signal in real time, so you can see exactly what’s triggering compression.

Stereo Operation

Stereo Link ties the two channels’ detectors for centered, mono-locked compression on stereo material. With link off, the channels operate independently for unlinked stereo or dual-mono use.

Oversampling

Kaiser-windowed 96-tap FIR oversampling at x2, x4, or x8, with phase-aligned dry-path delay compensation so parallel mixing stays perfectly time-coherent. x8 is recommended for mastering and detailed harmonic work.

Mix (Parallel Compression)

A dry/wet Mix control (0–100%) for built-in parallel compression — push deep gain reduction and blend in the dry signal for New York-style upward compression while preserving transients.

Metering

Authentic VU meter with switchable display: GR (gain reduction, needle pinned at 20VU at maximum compression) or OUTPUT (output level). Per-channel readouts for stereo monitoring.

20 Factory Presets

Default · Gentle Leveling · Vocal Smooth · Vocal Presence · Vocal Control · Broadcast Voice · Bass Glue · Bass Punch · Acoustic Guitar · Guitar Sustain · Drum Room · Drum Crush · Keys Warmth · Mix Bus Glue · Master Gentle · Master Warm · Heavy Limiting · Parallel Crush · Lo-Fi Vibe · Vintage Warmth.

Format & Compatibility

VST3 and AU, 64-bit, Windows and macOS (Universal Binary, Apple Silicon native).