Hi, I’m new here. I am planning on auditioning as a string player, and I’m narrowing down my college list. Out of the following schools, which would be considered the "most competitive, “middle tier”, and “less competitive” for string auditions?
University of Michigan
Washington University St. Louis
Emory University Atlanta
UCLA, UC Berkely
Carnegie Mellon
University of Virginia
Tufts
University of Rochester
Boston University
Tulane
Case Western
Le High
Pepperdine
Are you planning on auditioning as a music major at these schools?
UMich, Eastman school of music at URochester, Carnegie Mellon and Boston University would likely be the most competitive schools for music majors on that list if that is the case. I don’t know much about being a music major at the other schools on your list, maybe some other posters will know. Tufts has a dual degree program with NEC where the BM degree is pursued at NEC that is highly competitive.
Are you primarily interested in a BM music major or a BA? You would audition for a BM program but often a BA music major applicant does not have to audition for admission (though they might audition for orchestra or ensembles in the fall),
Your list is a mixed bag in that regard. Tufts, for instance, has a music major but not a BM program with auditions. (They do have a BM music degree with NEC).
Are you applying to Eastman or just U. of Rochester? BU itself or the BU School of Fine Arts> Ditto Michigan.
I am not going to look up each school but wonder what you are actually looking for 
I am looking to audition as music performance major, but not at a conservatory level school. (I know some schools such as UCLA only offers BA for music majors but they have a wonderful program)
Is UMich more competitive than UCLA for string auditions? I noticed that UCLA has a lower acceptance rate
A number of the schools on your list are non audition for admission as an undergrad, and only offer a BA in Music and not specifically in performance. They would have music classes one can take, and ensembles in which one could perform - but one needn’t even be a music major at all for that. My recommendation is, if you don’t want a competitive conservatory level don’t apply to a college with an auditioned program in a school of music, but just a department where you can subsequently declare a major or just take lessons and perform.
As for Michigan and UCLA - they’re comparable. If you live in California and are looking for a slightly less competitive BM in music, check out UC Santa Barbara, or the CSU’s which have many strong music programs. There’s also University of the Pacific. If you’re into Christian schools like Pepperdine you might look at Biola.