The result of one signal or waveform being modulated by another (or others). When a signal is either frequency modulated (FM) or amplitude modulated (AM) by another signal sum and difference frequencies are produced that appear with the signal. These are known as sidebands. The Upper Sidebands (USB), which are the result of adding the signals together, and Lower Sidebands (LSB), which are the result of subtracting them. Sidebands are a phenomenon that occur in FM and AM radio stations, but they are most relevant to us because they are a phenomenon that occurs in FM Synthesis. They are a big part of what gives FM synthesizers their unique sound.