In this work we develop an integral representation for the partial L-function of a pair π × τ of genuine irreducible cuspidal automorphic representations, π of the m-fold covering of Matsumoto of the symplectic group Sp 2n , and τ of a certain covering group of GL k , with arbitrary m, n and k. Our construction is based on the recent extension by Cai, Friedberg, Ginzburg and the author, of the classical doubling method of Piatetski-Shapiro and Rallis, from rank-1 twists to arbitrary rank twists. We prove a basic global identity for the integral and compute the local integrals with unramified data. Possible applications include an analytic definition of local factors for representations of covering groups, and a Shimura type lift of representations from covering groups to general linear groups.