http://www.mp3-box.org/mp3-to-aac/

what’s the best audio format that still has good quality when compressed to a smaller file? Ogg aac mp3 or wma?
i’m just asking
oh and the bit rate should be 48kbps
so what’s the best audio format at the best quality and the smallest file in that bit rate?
While 48kbps isn’t recommended for music, due to a lack of dynamics and such (the audiophiles would have a fit!). The best filetype would definately be Ogg Vorbis.
Ogg Vorbis, being open source, is a free codec to use. But not all players can decode Ogg Vorbis. So the next best choice would be MP3. EVERYTHING plays MP3.
Infact, you could have a higher quality Ogg Vorbis file, with the same amount of space taken up as a 48kbps MP3 file ;D
How to Convert mp3′s to “.aac” (for Nintendo DSi Music)