The Department of Music hosts many performing ensembles and combos. Participation is not limited to Music majors, but auditions are required. Some ensembles are open to community members. If you are new to Stanford, you will have to audition, regardless of whether or not you submitted a supplemental audition. Some ensembles require students to audition each year.
Audition procedures vary from ensemble to ensemble. Consult the Ensembles page for details.