And @old_music_prnt - there are only a small number of music schools that do ED- Frost, Ithaca and NU are three that come to mind. Oberlin and CMU do not offer ED as an option for performance majors.
With NU and Ithaca (the only two I am familiar with in this regard), the process is the same as RD, just earlier. They submit their applications and prescreen materials at an earlier deadline, and are invited (or not) to audition in late November. Admissions results are released mid-December.
The two voice majors I know who applied ED to NU were both accepted, so I can’t say if the defer many to RD. I do see on these boards that Frost commonly does that.
I am not personally in favor of ED as these students are 17/18 years old and ED removes any flexibility to make a decision with a much bigger picture come March/April when RD results are released. But, the two I know are very happy at NU and knew they wanted to attend.