The resources page is an excellent place to identify major repositories of oral history collections.
This subscription database from Alexander Street Press provides in-depth indexing to more than 2,700 collections of Oral History in English from around the world.
Using the Advanced search, limit the format to "sound recordings" then search on "oral history" under Keyword to find oral history collections. Add additional Author or Subject terms to focus results.
Audio materials include everything from oral histories, to music, to speeches, to radio broadcasts, and testimony and encompass all varieties of recorded sound. As with other types of sources, it is not just the format of the item that determines whether it is a primary source, but how it is being used.
For example, a radio broadcast of a scientist's explanation of how solar energy works would be considered a secondary source if you are using the text of what is said as evidence for your research. If, however, you are analyzing different ways to explain solar energy or examining a radio network's science coverage, the broadcast itself would be a primary source.
Interviews and Oral Histories (first-person accounts of lives or events) make excellent primary sources. Not only are you listening to someone's personal recollections, opinions, or interpretations of events they were directly involved with, you are hearing it in their own voice. Listening to a person's voice brings you closer to what they are saying than you can get by reading a transcript. You'll hear accents and inflections and gain a better sense of someone's personality when you hear them speak than when you read what they said. Consider conducting your own interviews and using them in your research.
Listen to an example from Story Corps.
Audio recordings, whether of music, speeches, radio broadcasts, interviews, testimony, or performances allow you close access to events, people, and movements throughout history. Recordings related to contemporary and historical events are available in libraries and online through such sources as the Internet Archive and the Library of Congress, to name just two.
Hearing evidence allows you to think about your topic in a new way.
You can study music just as you might examine and interpret a novel or painting as a primary source. Sonic art, soundscapes, and other uses of sound as artistic expression can aslo be considered to be primary sources.
Just as you must carefully evaluate what you read, you must also carefully evaluate what you hear.