Phase Shifting and Time Delay

Phase shifting and time delay are closely related. The first one is a process that occurs when a sound wave is reflected. These reflections might happen for several types of waves, including those on strings and light. The second refers to the process that records an input signal to a storage medium and then plays it back after a period of time. Both of these are essential in every equalizer or audio filter.

You can note that they 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. 

Phase Shifting and Time Delay: Some Examples

There are many examples of both concepts. All-pass filters are the most important part of phase-shifting effects. The reason is they can create an artificial stereo sound, which is the product of a mono sound source. Similarly, the flanging effect generates the same results by using a simple time-delay instead if phase shifting. 

All About the Waves

Sine waves involve the phase-shifting effect as well. The lower sine wave begins at the same time as the upper one. An all-pass filter sends it. 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 the all-pass filter added.

Within the music universe, when several frequencies go through either an all-pass filter or a time-delay period, the delayed audio mixes with the original version. When the user combines the original audio with its delayed version, the frequency response changes. While one cycle of the wave increases, the delayed version tends to fall. In contrast, when both cycles combine, they stop at the exact same frequency.

More on How They Work 

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 does not change, but the sound increases in both dimension and width. 

Phase shifting produces sounds that originate from a point beyond the physical location of the speaker. For example, the audible result might be similar to the one produced by a Leslie sound speaker. All depends on the amount of the phase shift. The reason is that both processes involve the creation of a phase shift and frequent varying time-delays through the vibrations of the speaker driver. 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. You can achieve the exact same effect when phase-shifting varies over a period of time.