Four ingredients.
Each feature is scaled and capped at 100. The default index is their weighted average:
35% density + 30% simultaneous notes
+ 20% high register + 15% leaps
- Density: note events per quarter beat, divided by 8.
- Simultaneous notes: percentage of onsets with multiple notes, divided by 60%.
- High register: percentage of notes at C6 or above, divided by 50%.
- Leaps: average semitones between the highest notes of consecutive onsets, divided by 12.
Playback tempo is excluded. Passage bars count note starts in 16-quarter-beat windows; they are not measure numbers.
What the corpus supports.
25 movements across 9 works have verified solo-track analyses: Bach, Beethoven, Tchaikovsky, Rieding, Telemann, and Vivaldi. A further 9 catalogue works include Sibelius, Lalo, Mendelssohn, Bruch, Brahms, Saint-Saëns, and Mozart.
Catalogue entries have official diploma placements but no verified symbolic solo parts here yet. They receive no numerical index.
Published ratings retain their original scope: a movement, a whole work, or a specified selection. Diploma categories are never converted to invented numbers.
No trained grade predictor is shipped. The current labels are too few, and edition review remains pending. Similarity finds nearby feature patterns, not an equivalent exam level.