Think Wikipedia, but with more credibility. While more recent encyclopedias may serve you well, do not forget to look at some of the oldest ones as well. Older encyclopedias and dictionaries can occasionally focus on different aspects of music than newer ones and may also mention some of the more obscure parts of music that are not as frequently studied in the present.
Baker's biographical dictionary of musicians
by
Baker, Theodore
Die Musik in Geschichte und Gegenwart: allgemeine Enzyklopedie der Musik
by
Blume, Friedrich
The encyclopedia of popular music
by
Larkin, Colin
Musical instruments: a comprehensive dictionary
by
Marcuse, Sibyl
The Harvard dictionary of music
by
Randel, Don, ed.
The Harvard biographical dictionary of music
by
Randel, Don, ed.
The new Grove dictionary of music and musicians
by
Sadie, Stanley, ed.
The international cyclopedia of music and musicians
by
Thompson, Oscar