mp3, or audio platforms in blockchain place are available, like Dsound, though they are connected to STEEM as well, and in the passed (and maybe still today) their service wasn't that stable. Not sure if you can upload a mp3 format though, maybe it needs to be a different audio format; Never used it myself tbh. Emanate on EOS blockchain is a hyped platform lately. Audio as far as I know. Aurovine is an older one as well. I think LBRY is audio as well. Am pretty sure many others are around, but most of them will have very low number of active users.