Historic materials or Primary Source materials are documents or manuscripts contemporary to a specific period in history. For example, the original manuscript of Igor Stravinsky's Rite of Spring is considered to be the primary source of information of the piece; an edited and printed version is a secondary source.
Additionally, a musical review published just days after the première of Rite of Spring is considered to be a primary source of information. An article published in 2009 summarizing the critical response to the Rite of Spring is a secondary source.
The key to finding primary sources is to match up the historic dates you are investigating to the dates covered by the database. The largest and most comprehensive historical indices and collections have been listed here to assist you in this type of research.