On the sibilance problem in FM sound transmission

An explanation for the sibilant distortion on FM sound transmissions is given. According to the proposed model, the effect is due to an overmodulation of the FM carrier, where the instantaneous frequency is proportional to the modulating signal. Pre-emphasis makes the effect worse, and the broadcast peak program meters (PPMs) do not indicate peaks in random signals. The explanation is backed up by simulation results and circumstantial evidence. A solution to the problem is offered: by clipping the signal after pre-emphasis the chances of overmodulation can be minimized