Radio broadcasting is transmission of audio (sound), sometimes with related metadata, by radio waves intended to reach a wide audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based radio station, while in satellite radio the radio waves are broadcast by a satellite in Earth orbit. To receive the content the listener must have a broadcast radio receiver (radio). Stations are often affiliated with a radio network which provides content in a common radio format, either in broadcast syndication or simulcast or both. Radio stations broadcast with several different types of modulation: AM radio stations transmit in AM (amplitude modulation), FM radio stations transmit in FM (frequency modulation), which are older analog audio standards, while newer digital radi