About .ntm vs .mid + Overdub + Speed
.ntm - Note Tuning Music - Full, recommended. JSON file. Saves notes + voice NAME + Ref + Temperament + Root + Scale + Chord + ChordOnly + mid-track changes + continuous pitch curve + volume curve.
.mid - Legacy, limited. Saves notes + velocity + one program change only. It loses tuning, temperament, Ref, voice names, and curves. Sine and piano both become program 0.
Speed / Octave - Tape varispeed: 0.5x = half tempo, freq / 2, octave down. 1x = normal. 2x = double tempo, freq * 2, octave up. This is like slowing a tape down or speeding it up. It does not change the saved .ntm, only how it plays back.
Overdub: In PERFORM, tick Overdub, then press Start Rec while PLAYER is playing. PLAYER keeps playing as backing, volume ducks to avoid clipping, new notes line up on same timeline. If Overdub is off, PLAYER stops when you hit Rec.
Freq formula: freq = ref * 2^((midi-69)/12) * 2^(cents/1200), cents from TEMP_MAP[temp][semi]. For Gliss OFF/OFF mode, continuous freq from baseMidi = 24+root+curved*84.