Amplitude modulation (AM) is one of several ways information is transmitted and received wirelessly using electromagnetic radiation. To transmit data or analog audio, a constant electromagnetic wave (carrier wave) is first produced. Then the amplitude of this wave is modified in a specific pattern which may be translated back into audio or other data at the receiving end. Amplitude modulated signals tend to travel line-of-sight from the source. They also can be interfered with by lightning. For these reasons as well as others, frequency modulation is sometimes a preferred method of communication. Another form of modulation, phase modulation, conveys information by instantaneous changes in the carrier wave's phase, rather than amplitude or frequency. Phase modulation is the basis of many digital communications standards, such as WiFi.