One of the important open problems in the theory of central simple algebras is to compute the essential dimension of GLn /μm, i.e., the essential dimension of a generic division algebra of degree n and exponent dividing m. In this paper we study the essential dimension of groups of the form G = (GLn1 × · · · ×GLnr )/C , where C is a central subgroup of GLn1 × · · · ×GLnr . Equivalently, we are interested in the essential dimension of a generic r-tuple (A1, . . . , Ar) of central simple algebras such that deg(Ai) = ni and the Brauer classes of A1, . . . , Ar satisfy a system of homogeneous linear equations in the Brauer group. The equations depend on the choice of C via the error-correcting code Code(C) which we naturally associate to C. We focus on the case where n1, . . . , nr are powers of the same prime. The upper and lower bounds on ed(G) we obtain are expressed in terms of coding-theoretic parameters of Code(C), such as its weight distribution. Surprisingly, for many groups of the above form the essential dimension becomes easier to estimate when r ≥ 3; in some cases we even compute the exact value. The Appendix by Athena Nguyen contains an explicit description of the Galois cohomology of groups of the form (GLn1 × · · · ×GLnr )/C. This description and its corollaries are used throughout the paper.