VGMTrans

VGMTrans is a music tool for Nintendo DS roms. With it, you can convert the music in the ROM to MIDI, .wav, and DLS. The DLS ripping is a unique feature of the program.

Download link: https://github.com/vgmtrans/vgmtrans/releases

Rip Sound Banks to DLS
You can create DLS bank files from the ROM. If you load the DLS into a compatible program (i.e. the free Modplug Tracker or the commercial FL Studio), you can play and create MIDI files with the sounds and instruments straight from the ROM. This is the main method for ripping DS music. Full tutorial here:

Real-time preview
You are presented with a large list of songs whenever you open a DS ROM. Instead of guessing what each song is, you can preview each song, as if it were played on the Nintendo DS.