Reference sources provide factual or essential background information.
A good starting point: Music Online Reference.
Music Online: Reference is a collection of over 169 e-book resources focusing on African-American, classical, and world music.
Next source to check: Oxford Music Online.
Supplement these e-references with print reference, found in Bishop Library, and listed in the center box.
Image Source: Koobak. CC BY-SA 3.0. Wikimedia Commons.
ALL of the reference resources below are found in either Music Online Reference or Oxford Music Online.
The New Grove Dictionary of Music and Musicians
The Oxford Companion to Music
The Oxford Dictionary of Music