Ahh this is a great article, thank you for the sources. 
I always had trouble finding the right music while working. Much of the music I love includes lyrics or progressive beats.. but those end up making me jittery and unfocused while coding.

But recently I stumbled upon this gem of a website called Brain.fm. It streams music that makes me Zen focus in about 5–10 minutes.

It generates original music that legitimately alters your brain waves to get your desired state — whether you want to deep focus (like coding), relax focus (like drawing/reading), relax completely, meditate, or even sleep.

Their goal is to eventually aid in curing ADD, anxiety, and insomnia. But the music definitely calms you and is very effective.

You can listen to 7 sessions for free.. and then have to pay like $4 a month. But it is honestly just as important as my Spotify subscription, if not more important.

I have absolutely no affiliation with this company or website, but it has really improved my life, my mindset, and my work, so I’m sharing in hopes that it can help somebody else too :)