The Reason Song Upload Options Vary Between Songwriter & Artist Accounts
Songwriter Accounts allow Mp3 and WAV audio uploads. The idea is that the quality of the file is not as important on the Songwriter Account because the song audio can be more of a "demo" in Mp3 quality. Songwriters just need to be able to let Artists and Publishers hear what the song sounds like. These audio files are not intended to be heard by fans. Mp3's have a smaller file size which saves Rhythmic Rebellion money on storage cost, but if you're signing up as both a Songwriter and an Artist, you only need to upload a song's WAV file once!