Phase Shift ○｜Definition｜1st｜20260908185746-00-⌔

Phase (waves) - Wikipedia#Phase_shift

Phase shift

🖼️ ➺ 🖼️ ➺

The difference $\phi (t)={\phi }_G(t)-{\phi }_F(t)$ between the phases of two periodic signals $F$ and $G$ is called the phase difference or phase shift of $G$ relative to $F$.¹ At values of $t$ when the difference is zero, the two signals are said to be in phase; otherwise, they are out of phase with each other.

In the clock analogy, each signal is represented by a hand (or pointer) of the same clock, both turning at constant but possibly different speeds. The phase difference is then the angle between the two hands, measured clockwise.

The phase difference is particularly important when two signals are added together by a physical process, such as two periodic sound waves emitted by two sources and recorded together by a microphone. This is usually the case in linear systems, when the superposition principle holds.

For arguments $t$ when the phase difference is zero, the two signals will have the same sign and will be reinforcing each other. One says that constructive interference is occurring. At arguments $t$ when the phases are different, the value of the sum depends on the waveform.

Printed 2026-09-08.

(echo:: @ ᯤ)

Footnotes

1. Ballou, Glen (2005). Handbook for sound engineers (3 ed.). Focal Press, Gulf Professional Publishing. p. 1499. ISBN 978-0-240-80758-4. ↩