Put a General MIDI SoundFont (.sf2 file) here: the packs' MIDI (.mid) music plays through it. Any General MIDI SoundFont you have works.
No SoundFont comes with the program. A free one: FluidR3_GM.sf2 by Frank Wen (MIT licence, about 140 MB):
search the web for "FluidR3_GM sf2", or on Linux install the fluid-soundfont-gm package (it puts the file in /usr/share/sounds/sf2).
The first .sf2 here (by name) is used
the launcher's SoundFont row can choose another file. More: docs/PACKS.md.
