MLA

Koch, Frederick R. (Frederick Robinson). Music/Improvisations on an Impromptu of Benjamin Britten. Box 293, folder 1635. [1970]. https://collections.library.yale.edu/catalog/2077443.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 293, folder 1635"])([1970])[Music/Improvisations on an Impromptu of Benjamin Britten]. https://collections.library.yale.edu/catalog/2077443.