--I'll try to update it to ndsp as soon as I can-- Simple sound example. Code primarily isolated from Marco D's Non-Stop Nyan Cat, huge thanks to him! =D (https://gbatemp.net/threads/release-non-stop-nyan-cat-smile-please.387427/) The sound file must be in raw Mono Signed 16-bit PCM format and at a frequency of 48000Hz (all of this can be changed at line 61). Just open an audio file on Audacity and export it as an "other uncompressed files", and press options to set its format, then export.
Also, place the "audio" folder on the same level as the .3dsx, not sure about on cia files, probably at the sdcard's root.