Oops went back to close the Stanford page and saw this in small print under the above:
“For information about preparing an Arts Portfolio in Music, visit our department’s Arts Portfolio FAQ page. In many performance areas, we are able to offer a live audition, if desired. (The two types of audition are given equal weight, but please choose one.) For detailed requirements for recorded or live auditions, find the appropriate link below.”
These “auditions” are considered part of the music supplement to the Common Application. They are supplementary (in a conservatory or music school they are central). The live auditions aren’t given more weight than recorded ones. The supplement/portfolio also includes a music resume and letter of recommendation from a music teacher. You need a Common App ID to submit an audition request.
Every school is different! Again these are optional…and you don’t have to be a music major at all.