Here's a neat lil hombrewed app from King Dodongo, Zelda SFX is a DS application that contains all the nostalgic Zelda sound effects and one background music, letting users to sample and play around the audio. Unfurtunately though, since the app is still on its early stage, you won't be able to record your creation or compose some tracks, but the dev plans to add some more features in future updates.

Developer's note:

Zelda SFX is a collection of all Sound effects and (currently) 1 background music.
I plan to add all bg-musics and more options
(currently options: volume,speed,pitch)

Controls:

• touch the buttons - play sfx/music
• Press UP/X - show/hide edit-mode
• Press DOWN/B - stop music