I haven't written anything fictional in a while (specifically screenplays), but I found that music was a distraction (especially if it had lyrics). I used playlists to set up a series of emotions that matched the storyline, but I listened to the music before, nor during, the writing process.

I did experiment with creating drones that I enhanced using using brainwave entrainment software to invoke concentration and focus (beta frequency) WHILE writing, and it worked pretty well. You can find a lot of beta and gamma frequency music and tones on YouTube to play around with. Here's an example (works best with headphones): https://youtu.be/HA6nSQawROM