Processing: 'Auto' transposes one-sample presets, chords are measured at their root note

[douglas-carmichael]

The Transpose processing option set to 'Auto' (#477) needs at least three measured zones which agree, so a multi-sample of one or two zones - typically one recording stretched across the keyboard - never got a result. 36 of the 50 synth presets of Rephazer's 'Operator's Choise' for the Deluge are such presets, and 26 of them sound one or two octaves below their root keys: 'R921 KEY RHODES NOTE' maps its recording of the MIDI note 84 (C6.wav, 1047 Hz) to the key 96 (transpose="-36"), so the Deluge plays it an octave below the keys as well. With 'Auto' selected none of them moved, and the note about presets which play their samples as recorded far from the middle of the keyboard (#288) still said that "the Transpose processing option can move it" - but set to 'Auto' it does not: 'Auto' moves root keys onto the measured pitch, not towards the middle of the keyboard.

Measuring the one-sample presets brought up a second problem, which affects multi-samples as well: a chord is measured an octave or more too low. Its notes are harmonic series of their own, and the only fundamental which explains all of them lies below the lowest note and does not sound - an octave below a fifth, two octaves below a major triad. 'Auto' then moves the dyads and fifth pads an octave too far: 'R919 DYAD LEGATO SYNTH 3' (F4 and C5) by two octaves instead of one, and 'LOFI 5TH PAD1' of Rephazer's 'Toneworld Vol. 3' for the Tonverk, whose 12 zones sound at their keys, by an octave.

Changes

• PitchDetector.detect: a multi-sample with fewer than three zones gets a result if all of its zones are measured, they agree and their offset rounds to a whole number of octaves (rounded like the transposition). A single recording has no other zones which could outvote a misreading; a root key set in another octave than the recording is the common case, and moving it by octaves keeps the keys in tune, while a chord or an inharmonic sound can measure as any interval. Multi-samples of three or more zones are measured as before.
• PitchDetector.findChordRoot: when the found fundamental does not sound (less than 3% of the power of its strongest harmonic), its harmonics up to the last audible one (at most 24) are checked. Every harmonic which belongs to none of the notes found so far must either be missing (below 0.1% of the harmonic power or 3% of its neighbours) or start the series of another note (at least 2%). Two or three notes with at least two missing harmonics besides the fundamental are a chord - a fifth leaves the harmonics 1, 5 and 7 empty, while a single note whose fundamental is weak or filtered away still has them; anything else stays a single note as before. The chord is measured at its note at the pitch class of the fundamental - the harmonic 2, 4 or 8, which is the root of a fifth, a fourth, a major third and a major triad in all of its inversions - and a chord without such a note is not measured. A reading therefore only moves up by whole octaves or disappears; its pitch class never changes.
• ConverterBackend.checkOffCenterMapping: the note names the setting of the Transpose option which plays the samples as recorded closest to the middle of the keyboard, in whole octaves within its range of ±24, and says what 'Auto' does - e.g. "The Transpose processing option set to +24 plays them as recorded at C4 (MIDI 72) - set to 'Auto' it only moves root keys onto the pitch measured in their samples." It is only logged when the processing left the middle of the keyboard as the source maps it: a multi-sample which was transposed, by a fixed number of semitones or by 'Auto', no longer gets it.
• ConverterBackend.checkSamplePitch: analysing with 'Auto' selected reported no pitch at all. The note was left out because the transposition reports it, but analysing does not transpose.
• README (the paragraph about 'Auto') and CHANGELOG (the bullet of Processing: the samples can be transposed onto the pitch they sound at #477 and a bullet for the note).

Verification

• 'Operator's Choise' converted to Waldorf QPAT with -Ze -Zpa, with main 31b0f8a and with this branch: main moves 2 multi-sampled presets and logs 32 notes about the middle of the keyboard; the branch also moves 26 one-sample presets - 4 by 24 semitones and 22 by 12, among them the dyads 'R917' and 'R919' - leaves 'R926 LEAD 101 SAW' (-11.5) and the dyad 'R918' (-28.1) alone, and logs 9 notes. Only the QPAT files of the 26 presets differ, in the pitch column of the sample map and nowhere else except the length of the map of 'R931', whose pitch goes from 101 to 77; all samples are byte-identical.
• Analyse of 597 presets of 10 libraries before the first commit, after it and after the second: 'Operator's Choise' (Deluge), Rephazer 'Toneworld Vol. 1-3' (Tonverk) and 'XY Classic Rompler' (OP-XY), Espen Kraft 'DX Dreams' and 'PX Vol 2' (SoundFont) and his TAL-Sampler collections Vol. 1 and Vol. 4, and the program library of the 3rd Wave. The first commit adds readings only in libraries of one-sample presets (Toneworld Vol. 3: 13, TAL Vol. 1: 47, 3rd Wave: 2) and changes no other; spectra of the analysed segments confirm them, e.g. 'D-50 Alice Bells' of TAL Vol. 1 sounds at 522 Hz with its root key at 60. The second commit changes 10 presets: 2 dyads, 2 fifth pads and the fifth 'FADERS PATH' (Toneworld Vol. 3) are measured an octave higher; the zones of 'LOFI 5TH PAD1' now agree that it sounds at its keys and those of 'LOFI 5TH PAD3' no longer agree on a wrong octave; the top zone of 'Bass Drone' (TAL Vol. 4) holds a fifth and now agrees with the other two; 'CLOCKENSPIEL' (Toneworld Vol. 1) and 'Organ 2' (TAL Vol. 4) keep their result with one zone more or less which agrees. All other readings stay the same, among them single notes with a weak fundamental such as the horn 'R927' (0.6% of the power at the fundamental), the basses, and the FM bells of 'DX Dreams', whose harmonics 3, 4 and 5 look like a triad but whose other harmonics sound as well.
• A chord of more than three notes is not recognised: the choir chord 'Marine vocal 3' of the 3rd Wave program 'Poly Chord Marine+Kurt' (B♭3, B♭4, C5, D5, F5) is still measured two octaves below its root key.
• Built on main 31b0f8a.