Keep Quarter-Beat Time When a Score Has Eighth Notes

A developer building Pianory, a browser-based piano practice app, described how the app keeps a single quarter-note unit for musical positions and converts to seconds only when scheduling audio, so eighth notes don't disturb the metronome pulse. In an illustrative 4/4 bar, the two D4 eighth notes land at quarter positions 1 and 1.5 while the click grid stays at 0, 1, 2 and 3, with each note sounded at 96% of its written duration subject to a 0.06-second floor. The developer reported 39 passing tests across two spec files but noted the suite does not assert this exact eighth-note bar, calling a test for both D4 attacks a useful follow-up.

I build Pianory, a browser-based piano practice app. AI helped draft this article; I checked its code claims against the current source. A score can contain a quarter note on beat 1, two eighth-note attacks within beat 2, and quarters on beats 3 and 4. Playback needs to keep one unit for the musical positions and convert to seconds only when scheduling audio. Otherwise a faster note value can accidentally change the click pulse. Consider this illustrative 4/4 bar: C4 quarter, D4 eighth, D4 eighth, E4 quarter, F4 quarter. In quarter-note units the inferred event starts and lengths are 0, 1 , 1, 0.5 , 1.5, 0.5 , 2, 1 , and 3, 1 . The two D4 notes are distinct attacks at different positions. This tuple sequence is an example derived from the conversion, not a committed test fixture. Pianory's score source converts OSMD iterator timestamps and note lengths by multiplying whole-note units by four. Its timeline stores positions and durations in quarter-note units. At quarter-note tempo B, a quarter lasts 60/B seconds and an eighth lasts 30/B seconds. The metronome grid for a complete 4/4 measure still walks quarter positions 0, 1, 2 and 3, with the first beat accented. The player schedules each note at its converted audio time and uses a 96% written-duration sounding length, subject to a 0.06-second floor and passage-end clipping. That small articulation gap does not move the next note's written onset. I ran pnpm exec vitest run src/lib/sheet/player.spec.ts src/lib/sheet/timeline.spec.ts : 2 files, 39 tests passed. The tests cover quarter onsets, count-in and neighboring duration behavior, but do not assert this exact eighth-note bar or .5 duration. A useful follow-up test would assert both D4 attacks at quarter positions 1 and 1.5 while the click positions remain 0, 1, 2 and 3. That is a source-based expectation, not a measured audio-device result. Relevant source: src/lib/sheet/types.ts , src/lib/sheet/osmd-source.ts , src/lib/sheet/timeline.ts and src/lib/sheet/player.ts .