By applying a series of detailed approximations to the Rice and Bosse theory of f.m. intermodulation noise, the recent formulae of Medhurst and Roberts for intermodulation noise/signal ratios in f.m. systems with white-noise modulation and networks of polynomial frequency characteristics are extended in three respects: (a) to the calculation of the noise ratio at any modulation frequency, (b) to network real and imaginary characteristics of eighth and seventh degree, respectively, and (c) to the case of pre-emphasis. The theory is illustrated by application to the cases of a signal with C.C.I.R. pre-emphasis passing a stagger-tuned triple without and with groupdelay equalization.