An AM/FM receiver which demodulates radio signals by computing estimates of spectral parameters of the radio signals. Three spectral parameter estimation circuits are selectively formed from a number of shared circuits according to the type of modulation of the radio signal. In the case of frequency modulated signals, the respective strengths of the desired signal and interfering signals dictate the most favorable circuit configuration. The first estimation circuit calculates the instantaneous amplitude of the radio signal which corresponds to the modulating audio signal of an AM signal, the second estimation circuit calculates the instantaneous frequency of the radio signal which corresponds to the modulating audio signal of an FM signal, and the third estimation circuit calculates the power mean frequency of the radio signal which, when calculated over a short period of time relative to the rate of change of the FM signal, also corresponds to the modulating audio signal.