This paper proposes a new signal-to-noise ratio (SNR) definition for magnetic recording channels with both additive and medium noise components, The proposed SNR is a generalized version of E-b/N-o, the information bit energy to noise spectral height ratio, widely used in average-power-constrained communication channels with additive white noise. The goal is to facilitate comparison of efficiencies of read channels that may operate at different symbol densities because of varying code rates.