This is a guide to the use of pre-digital (analog) recordings in music research; i.e., cylinders, 78s, 45s, 33s. It will not cover CDs or downloads except as carriers for material originally captured in one of the formats above.
Early recordings are germane to several fields of study:
1. Performance practice. The early 20th century is the first period for which we can hear what music actually sounded like. While the technical limitations of early recordings somewhat compromises the information, still we can hear that the assumptions of musicians in 1910 were not necessarily those of modern performers.
2. Ethnomusicology. Collectors like Percy Grainger, Bela Bartok and Alan Lomax recorded folk music while it was still orally-transmitted, without the influence of recordings, radio, and print. Early recording companies knew there was money to be made in the ethnic market, but had no clear idea what they wanted, so they'd record a little of everything and see how it sold.
3. Social studies: sociology, politics, religion, etc. Recorded music, particularly popular music, gives us a window on history and attitudes.
In using early recordings, it is good to remember that, under current interpretation of US copyright law, there are basically no public domain recordings in the US, not even the Edison recordings, which were donated to the government in 1957. Federal copyright is for 95 years, but pre-1972 recordings are covered under state common law, which holds them as property in perpetuity. EU copyright has been for 50 years from date of release, but has recently been increased to 70 years (though each of the member countries has to ratify the change). Fortunately, recordings currently in the public domain there will remain so, but artists like the Beatles will not cease being considered the property of EMI. The conceptual legitimacy of intellectual property as property has been vigorously debated on the Internet. Under present law, there is a chasm between the needs of scholars and preservationists, and the needs of the recording companies and the law. Put simply, any digitization of a commercial recording not done by the copyright holder is probably a violation of copyright, and the archivist may be forced to choose between what is ethical and what is legal. Those who digitize and wish to share their files should be aware of current law.