I'm already a member of JACAP, ASCAP, BMI or SESAC. Don't they cover this for me? What is the difference?

No. ASCAP, JACAP, BMI and SESAC represent a different copyright than JAMMS. JACAP, ASCAP, BMI and SESAC collect performance revenue for the owners of the copyrighted musical work (the song), i.e. music publishers, songwriters and composers. JAMMS collects performance revenue for owners of the sound recording copyright (the recording). JAMMS, therefore, performs a different function and does not compete with ASCAP, JACAP, BMI or SESAC. In fact, an individual/label or company with both publishing ("song") copyrights and recording copyrights should join collecting societies administering both types of rights: one for the song and another for the sound recording copyright.