Amplitude modulation results in what in the spectrum?

Amplitude modulation is a process in which the amplitude of a carrier signal is varied in accordance with the amplitude of the input (or modulating) signal. When this occurs, the frequency spectrum of the modulated signal is altered in a specific way.

In the spectrum of an amplitude-modulated signal, the original frequency (the carrier frequency) will remain, but additional frequencies will be created. These additional frequencies, known as sidebands, exist on either side of the carrier frequency. Specifically, there will be an upper sideband and a lower sideband, which are spaced from the carrier frequency by the frequency of the modulating signal. The presence of sidebands is a key characteristic of amplitude modulation, indicating how the signal has been transformed due to the modulation process.

The development of sidebands is fundamental to understanding how information is transmitted in amplitude modulation, particularly in applications like radio broadcasting, where the information signal (voice, music, etc.) modulates the carrier wave, allowing the transmission of that information over great distances.