The waveform selection parameter allows the choice of the shape of the signal generated by the LFO. Typical shapes include sine, triangle (tri), square, and sawtooth (saw). The two most common waveforms used for vibrato or tremolo are the sine and triangle. The square wave is used for trills, and saw for special effects. Some LFOs offer a random (also called sample-and-hold) waveform, useful for “computer” sounds. See sound synthesis, Appendix C.