Baker's Biographical Dictionary of Musicians REF ML105.B16 2001
Dictionnaire de la musique REF ML100 .D65
Enciclopedia della musica REF ML100 .E45
Encyclopédie de la musique et dictionnaire du Conservatoire REF ML100 .E5
Diccionario de la música española e hispanoamericana REF ML101.S7 D53 1999
The Harvard Dictionary of Music REF ML100.A64 2003
Die Musik in Geschichte und Gegenwart REF ML100 .M92 1994
Open-access = FREE to download and or read online.
LC's digitized collection Books about Music before 1800 offers access to nearly tw0-thousand books about music printed before 1800. Early highlights include Johannes Tinctoris's Terminorum musicae diffinitorium (c1474), Franchinus Gaffurius's Theoricum opus musiche discipline (1480), and Henricus Glareanus's Dodekachordon (1547).
The Directory of Open Access Books' primary aim is to increase discoverability of Open Access books. Academic publishers are invited to provide metadata of their Open Access books to DOAB.
JSTOR's open-access titles include just over 40 books in music. Using the search box will list open-access journal articles and book chapters. If you want a list of book titles only, click on the "Download the title list" button and sort by discipline (music).