Credits
Umaro plays real recorded instruments. Thank you to the people who made these sounds freely available.
Piano
Salamander Grand Piano (Yamaha C5) by Alexander Holm — released into the public domain. Notes are pitch-shifted and run through Umaro's own reverb.
Guitars
The electric, acoustic and nylon guitar voices use samples by Nicholaus P. Brosowsky, from the tonejs-instruments project, licensed under Creative Commons Attribution 3.0 (CC-BY 3.0). The samples are pitch-shifted and played through Umaro's amp and effects chain. You can switch between them in Settings.
Drums
The hi-hats, ride, crash, snare and toms in the backing tracks are real recordings from the Versilian Community Sample Library by Versilian Studios, released under CC0 (public domain). Each snare and tom has several takes, so a roll rotates between them rather than repeating one recording. The kick is synthesized by Umaro in the browser.