This paper presents a means of modulating timbre in digital sound synthesis using additive processes . A major portion of the paper is a computer program, written in Pl/1, which combines this additive method of timbre modulation with several other sound manipulation ideas to form a compositional program. This program-which is named CART for Computer Aided Rotational Translation-provides input for the Music 360 digital sound synthesis program. The paper contains three major parts: (1) a discussion of the CART program's evolution; (2) a manual describing in detail the use of CART; and (3) two tape compositions realized using the program. An appendix contains the program listing and listing of the input cards that were used to produce the two compositions.