nx_note.nx

nx_note.nx -- AUDIO arc, INSTRUMENT-LEARN-GAME (Rocksmith-class) rung LG-0: turn a detected pitch into a MUSICAL NOTE. This is the bedrock of "what note are you playing?" for ANY instrument -- guitar, bass, piano, violin, voice -- because every pitched instrument lands on the same 12-tone-equal-temperament grid. Composes nx_pitch (F0) upstream. 12-TET: MIDI note m has frequency f(m) = 440 * 2^((m-69)/12). A4 = 440 Hz = MIDI 69. We build the note->frequency table by repeated multiply/divide by the semitone ratio 2^(1/12) (Q16), so no runtime log/pow is needed; nearest-note is a scan, and the in-semitone error is reported in cents (first-order, exact sign, ~1-cent accurate within a semitone). Pure integer, NO floats, NO syscalls, NO imports (caller owns all buffers). nx_note_table(tbl) -- fill tbl[0..127] with note freq in centi-Hz nx_note_of(f0_hz, tbl, out) -- out[0]=midi out[1]=cents out[2]=pitch_class (0=C..11=B) out[3]=octave (MIDI 60 = C4); returns midi, or -1 if f0<=0 license_tier: ORIGINAL module: nishi-core.audio.note depends: nishi-core.audio.pitch capability: AUDIO_NOTE_ID