The publisher is the owner or administrator of the copyright to a song not the sound recording. That just means the words and music: melody, harmony, lyrics.
If you or a songwriter/composer you know has never signed away their publishing rights to a publishing deal, then the songwriter IS the publisher.
However, don't get confused with a sheet music publisher or CD manufacturer. "Publisher" in the music world just means "copyright owner or administrator" of the song itself.
ASCAP, BMI, SESAC, Harry Fox, SOCAN - are NOT publishers. These are three companies in America that collect the broadcast ("performing rights") money for songwriters, so they can get paid for their music being used on radio and TV broadcasts. We don't need to know if a song is ASCAP or BMI when submitting your track information.