Using encyclopedias and dictionaries can help you develop your topic. Articles in these sources can help you narrow or broaden your topic to an appropriate topic for the length of your assignment. Generally, encyclopedias and dictionaries are not good as main sources of information so don't expect to cite an encyclopedia or dictionary very extensively.
Many of the databases listed below include a variety of types of sources including magazine articles, journals articles, book reviews, sometimes even electronic books. When writing research papers such as the one you are assigned, it is best to use journal articles and books (electronic or paper) as the majority of your sources. Articles published in journals have gone through a review process before they ever get published. That does not mean there are no errors in the articles so you must still evaluate the information you use, but the journal articles are considered more authoritative than many other sources of information.
The Garland Encyclopedia of World Music by 
The Grove Dictionary of American Music by Below is a selection of reference titles that you might find useful in developing your topic.
Musicians and Composers of the 20th Century by 
Baker's Biographical Dictionary of 20th Century Classical Music by