The Music Performance Research Centres (MPRC's) holdings consist of over a thousand hours of recordings. These are all archive-recordings, both audio and video, that is recordings that have not been made for commercial purposes; they cannot be purchased or borrowed. They are of public performances and conversations with performers, dating from the early 1930s to the present time, which at the time of going to press cover a period from 1933 to 1995. Nearly all these recordings do not exist in other archives. The performances are preserved without any editing. In 1948, the off-air' recording was made; the broadcast studio performance was very similar to a public performance in that it was continuous and not edited. Within a few weeks the same artists made a commercial studio recording of the opera. At March 1995, the MPRC had placed in its archive 170 performances recorded off-air' from broadcasts. All the recordings had been received as donations, including many historically significant performances.