Signal Archaeology — Optical Recovery & Media Forensics for Fragile Sound Carriers

Mechanical playback destroys what it preserves: a stylus exerts grams of force on grooves already fractured by age, mold and heat. Signal archaeology decouples recovery from wear. The division’s core apparatus — a 405 nm blue semiconductor laser projecting a knife-edge across a groove wall, captured by a high-speed linear CMOS sensor at 200 kfps — extracts stereo audio directly from surface geometry.

The raw scan contains music and damage together: dust fibers, mold pitting and handling fissures all modulate the sensor. Our contribution is artifact isolation via curvature invariants — intentional acoustic cuts obey acceleration limits set by original recording horns, while damage exhibits steep vertical edges. That distinction lets us flag and bridge faults without dulling transients. Case studies include 1898–1912 wax cylinders with indigenous oral poetry and laboratory tuning-fork tests recovered after being listed as “unplayable.”

Field deployments tie lab forensics to landscape listening: VLF radio loops at the Mojave and Atacama arrays monitor the electromagnetic sky, while optical scanning is tested on ceramic and glass fragments that were never intended to hold sound at all. Peer dossier ESSAY-2023-02 documents the method and four full restorations.

Media forensics method is published with replication tolerances. The 405 nm knife-edge, 200 kfps linear CMOS, air-bearing rotary stage with sub-micron axial runout, and dual-wall groove displacement math are all specified with part numbers and calibration against NIST surface-roughness standards (target Ra 0.02 µm). The curvature-invariant artifact filter is described algorithmically: groove walls are expected to follow continuous acceleration bounds set by historical cutting lathes; step discontinuities steeper than 85° vertical are flagged as damage, bridged with Catmull-Rom interpolation, and logged as provenance, not hidden.

Corpus is four restorations deep and cross-linked. ESSAY-2023-02 documents 1898–1912 cylinders with oral poetry and tuning-fork tests, each with before/after spectrograms, groove-topography stills, and listening excerpts where copyright permits. Field listening extends the same apparatus to non-grooved carriers: ceramic and glass fragments analyzed for accidental acoustic impressions, and VLF sky data from Mojave/Atacama arrays published as Datasets with distributionUrl. The discipline therefore offers both archival forensics and landscape acoustics under one instrumental logic.