All instrument sounds are real recorded samples (not synthesized), used under Creative Commons Attribution 3.0 (CC-BY 3.0):
Grand Piano — Salamander Grand Piano by Alexander Holm.
Bright Acoustic / Electric Grand / Honky-tonk / Electric Piano 1 — FluidR3 GM soundfont, via gleitz/midi-js-soundfonts.
Guitar, Bass, Strings, Winds, Brass, Organ, Harmonium, Xylophone — tonejs-instruments by Nicholas Brosowsky, originally sourced from Versilian Studios (VSCO2), Karoryfer Samples, Freesound.org contributors, and the University of Iowa Electronic Music Studios.
Full licenses, attribution text, and commercial-use notes: see COPYRIGHT_INFO.md in the app folder.