Types of primary sources used in music research include:
Many scores and recordings in the circulating physical collection are primary sources including manuscript facsimiles, audio recordings, and early printings. The search terms --facsimile or --sources can help you find them. Beyond these, the SCRC holds everything from medieval music manuscripts to an Oscar!
There are a few ways to locate facsimile images of manuscripts and early editions in the stacks of the library. Many printed scores contain images of specific pages of manuscripts in order to facilitate study of the work, and there are also entire manuscript works reproduced as a printed score.