An FM radio receiver usually has at least one stage of amplification for this purpose. It provides a constant level of signal to the FM demodulator stage, reducing the effect of signal level changes in the output. If two or more signals are received at the same time, a high performance limiter stage can greatly reduce the effect of the weaker signals on the output. This is commonly referred to as the FM capture effect.
Generally, FM demodulators are not affected by amplitude variations, since the baseband is contained in the frequency deviations. Some detectors, including the Ratio Detector, inherently limit gain by a nature of the circuit design. In AM radio, the intelligence is located in the amplitude variations, and distortion can occur due to spurious signals that could cause the baseband to be misrepresented.