Radio uses parts of the electromagnetic spectrum to transmit audio signals. AM radio uses amplitude modulation to vary the strength of radio carrier waves to encode audio information, while FM radio uses frequency modulation to vary the frequency of carrier waves. AM radio has greater coverage range but poorer audio quality and is more susceptible to interference than FM radio. The key differences are that AM modulates amplitude while FM modulates frequency, FM can filter out interference better, and FM provides higher quality stereo audio over greater distances.