Phase shifting is a process that occurs when a sound wave is reflected. These reflections might happen for several types of waves, including waves on strings and light waves. Both phase shifting and time-delay are essential in every equalizer or audio filter.
There are many examples of both concepts. All-pass filters are the most important part of phase-shifting effects since they can create an artificial stereo sound which is produced by a mono sound source. The flanging effect generates the same results by using a simple time-delay instead if phase shifting.
Phase-shifting and time-delay are similar concepts. Phase-shifting delays some frequencies for a longer period of time, while time-delay shifts frequencies by the same amount of time.
Sine waves involve the phase-shifting effect as well. The lower sine wave begins at the same time as the upper sine wave and is sent through an all-pass filter. When this happens, there is a time-delay of the frequency by 90º. The user is able to see both waves together and detect the time-delay that has been added by the all-pass filter.
Within the music universe, when several frequencies are passed either through an all-pass filter or a time-delay period, the delayed audio is mixed with the original version. When the user combines the original audio with its delayed version, the frequency response is modified. It’s worth mentioning that while one cycle of the wave increases, the delayed version tends to fall. When both cycles are combined, they stop at the exact same frequency.
When using an all-pass filter to create fake stereo, the user must apply phase shifting to the left and right channels in separate ways. When this happens, the frequency response is not modified, but the sound increases in both dimension and width.
Phase shifting is capable of producing sounds that originate from a point beyond the physical location of the speaker. The audible result might be similar to the one produced by a Leslie sound speaker depending on the amount of the phase shift. This happens because both processes involve the creation of a phase shift and frequent varying time-delays through the vibrations of the speaker driver. It’s worth mentioning that when referring specifically to the Leslie speaker, the Doppler effect causes the pitch to increase and decrease while the rotating horn driver moves back and forth. The exact same effect can be achieved when phase-shifting varies over a period of time.