Folding a Recording onto a Fundamental: A Pitch Codex for Field Material

A recording of an environment contains no played note, and yet a rule can be made to assign it one. This paper states that rule completely enough to be re-executed without access to any code, and freezes it as the Pitch Codex for Field Material, version 1.0. The rule takes a recording, optionally a range within it and a transposition in whole semitones, and returns one fundamental, twelve weighted pitch classes, and a spread — the strongest class divided by the weakest. Its eight parameters are named with the reason for each. Four rules tried and withdrawn are recorded with the measurement that killed each: folding onto twelve classes before a fundamental is chosen puts a low rumble and a high resonance in one bin; scoring a candidate by the sum of its harmonics lets sub-octave ghosts survive; removing the spectral slope removes the identity along with the bias; a single harmonic-series hypothesis returns a confident figure on material that has no fundamental at all. What the instrument does not do is set out at equal length: it names no chord, produces no chromatic coordinates, and reports no melodic line for a place — the last a decision rather than a measurement, since no threshold separating a margin that names a fundamental from one that does not has been stipulated. The spread is the quantity worth attending to: in the hundreds on a manufactured tone, between 1.2 and 3.8 on field material, and it reports the latitude the rule finds rather than a hierarchy belonging to the material. Two debts to the research notes are settled. The paper's triad of strata departs from Note 04 by replacing acquired technique with the given/instituted pair legislated in Note 05; and the condition Note 05 attaches to any measurable gap — that the arrival material carry a metric — is shown to be met here and empty, no hand standing between the rule and its output.