Radio tuner specification referring to how well a tuner is able to ignore changes in a FM (frequency modulation) signal’s amplitude caused by noise and signal anomalies due to interference. The amplitude of a signal refers to the distance from a signal wave’s base point or midpoint (its zero) to its peak on a wave. FM radios use a constant amplitude while varying (modulating) the frequency to transmit a signal. When the amplitude is altered from a constant state, noise is introduced degrading the signal quality and the final output. A FM tuner should be able to ignore changes in the signal’s amplitude. When this is done, the noise introduced in amplitude variations is discarded and not reproduced. Higher AM rejection levels are better.