The frequency spectrum of a typical modulated AM or FM radio signal is shown in the figure below.
The audio broadcaster's transmission can be a live stream, or it can be a pre-recorded advert. The adverts may be adapted to the specific context of each station. Moreover, the broadcaster can modify the frequency and/or amplitude of the radio transmission to match with a certain audience's interests. Likewise, the adverts can be adapted to the time of day or to the location of a listener. The ads can be inserted at the beginning or during a radio broadcast.