The phase of an audio signal is determined by where in a single cycle of a sound wave the amplitude starts. The phase of a sound wave can be switched to be 180 degrees out of phase using an electrical circuit. It can be useful to switch the phase of a single audio signal where two signals combine and cause phasing problems. For example, two audio signals form the ams source 180 degrees out of phase with each other can cancel each other out. Therefore it might be necessary to switch the phase of one of the signals.