depends on the task and also depends on the BPM.

Minimal music (with minimal changes and high repetition works for me, as it does not take too much focus away).

And for some reason the Ghosts from Trent Reznor, NIИ is my ultimate emergency focus medicine. 🙂

https://archive.org/details/NineInchNailsGhostsI-Iv24bit48khz/0101GhostsI.m4a