The program doesn't really run at a constant rate and keeps stuttering so the rythms are all over the place. Too bad because otherwise it seems like a cool concept.
Ah I'm sorry you're having that problem. The audio is scheduled accurately with the web audio api (using Tone.js), but on some devices performance could still be an issue. The best experience is definitely with Chrome or Firefox on desktop/laptop (Safari or mobile devices may not work as well). If you think your device should be capable of running it smoothly (or the frame rate is good, but the audio isn't) it could help me out to know which OS and Browser you're using.
Stutters at ~24 seconds, ~32, maybe 1:30ish, 5 seconds after that... then I lost track. Not very often but when it does it's very jarring. Happens if it's running in the foreground or background, even if I'm not moving around or anything, just listening with tab in focus.
I think it should run smooth because I can play minecraft at 1440p at around 100 fps.
For me the Mad World one stutters before a single note is played: the repeater/clock seems to run, then stop, then "catches up", then stutters again, then one cycle smooth, etc. Sometimes notes are also just skipped, or only the last part of the soundbite is played.
I looked at cpu usage and it pegs a single thread to about 90% so maybe that explains it.