When you submit a piece of Audio to Newgrounds, it will be made available instantly on your user page but will not appear in the Audio listings until your account has been approved by an Audio moderator. This process can take a few days so please be patient; we intend to change to a community-vetted system similar to the Art Portal.
Here are some details specific to audio submissions:
There is a file size limit of 15 megabytes.
Files must be sampled at 44.1 kHz.
Rappers, singers, lyricists and voice-over actors are encouraged to submit a capella tracks, or by using and crediting other NG audio as a base, as using copyrighted work is expressly forbidden.