Angle modulation covers frequency modulation and phase modulation; it has advantages over amplitude modulation in terms of noise performance. It is more difficult for noise to spoil the FM signal since noise is usually additive and affects the signal amplitude only. An FM signal with corrupted amplitude is easier to demodulate than an AM signal; we pass it through a limiter to obtain a constant amplitude signal before passing it to a discriminator. The price for improved noise performance is a signal bandwidth wider than the AM case. When FM or PM is used for data communication, it is called an FSK or PSK signal.