Missing the build-up therefore lacks the sync to the music.

HTML Canvas speed differs hugely between browsers/devices. Smartphones/Tablets have relatively poor performance compared to desktop machines. I'm getting the best results running Chrome on my notebook. Runs at stable 60FPS on my machine (UPDATE: even on my smartphone ... so I'm a little confused, why this - not too complex - intro performs that bad on your side) . You can check your framerate by adding "?fps=1" to the URL (https://www.docsnyderspage.com?fps=1) . What is the framerate you are getting? And what device/OS/browser do you use?

Runs way too slow therefore does not fit to the pace of the music.