When an LFO modulates amplitude (volume), it creates tremolo. On most synthesizers and sound modules, LFOs feature several controllable parameters, which often include a variety of different waveforms, a rate control, routing options (as described above), a tempo sync feature, and an option to control how much the LFO will modulate the audio signal. LFOs can also be summed and set to different frequencies to create continuously changing slow moving waveforms, and when linked to multiple parameters of a sound, can give the impression that the sound is "alive".