Lumen

Lumen is Greybound's first compressor model. The reference target is a high-end optical/tube-style leveling amplifier adapted for the front of a guitar rig: smooth gain reduction, musical sustain, low artifact level, and a sidechain that avoids excessive low-end pumping.

It is not a literal studio rack clone. The implementation keeps the useful behavior for a guitar pedalboard: high input impedance, guitar-level headroom, a faster front-end attack than a pure LA-2A, program-dependent optical release, tube-style softening, sidechain voicing, and parallel compression.

Reference Placement

The reference rig places Lumen first in pre_amp:

• guitar/source loading through ConnectionState,
• high input impedance at the first pedal boundary,
• compressed signal drives fuzz, overdrive, distortion, and amp input consistently,
• low output source impedance into the next chain slot.

This is the default guitar-rig placement. Later studio-style post-amp leveling can reuse the same model in another rig section if needed.

Controls

• peak_reduction: amount of optical gain reduction.
• gain: makeup/output gain.
• emphasis: sidechain voicing; higher values make the detector less dominated by low fundamentals.
• mix: dry/compressed blend for parallel compression.
• bypass: routing state; detector and optical memory remain private to the pedal instance.

DSP Mapping

• Input boundary uses ConnectionState with high input impedance and cable capacitance.
• Input coupling removes DC before detection and audio processing.
• Sidechain high-pass emphasis lets the detector respond more musically to guitar.
• Detector maps level above threshold through a soft knee.
• Optical memory smooths gain reduction with faster attack and program-dependent release.
• Makeup gain restores level after gain reduction.
• A mild tube-style saturating stage rounds the compressed path.
• Dry/compressed mix preserves pick transient if desired.
• Output is clamped and exported through a low output source impedance.

Validation

Current validation is behavioral:

• high peak reduction reduces the loud/quiet ratio versus the open path,
• active pre-amp chain output remains audible,
• rig parser accepts all Lumen controls,
• CLI runtime controls are shared atomics so the monitor can edit peak reduction without locking the audio callback.

Useful next checks:

• render transient files at different peak_reduction values,
• plot gain-reduction envelope from a pulse train,
• compare Lumen before and after fuzz/overdrive in full rigs.