Phase velocity measures single-frequency speed while group velocity tracks the signal envelope

Evidence

“Phase velocity” is the correct term for what we have, so far, simply called velocity. It’s the speed at which a single frequency travels through the medium. It’s called phase velocity because it describes how fast a particular part of the sine wave’s phase, e.g., the crest or zero crossing point, travels through the medium. It is given a distinct name because in dispersive media the phase velocity varies with frequency. This gives rise to two different velocity measures: The phase velocity for the individual frequencies and the group velocity for the envelope of the signal. — David Howard, Jamie Angus, coustics and Psychoacoustics, 105

Categorization

• DEFINE: Clearly distinguishes phase vs group velocity and ties the distinction to dispersion — foundational for understanding how complex signals propagate.
• XREF: Connects to how a struck string or drum produces a tone that decays — dispersal of partials over time; also to how sound localizes differently for transient vs sustained sources. — connects to: Longitudinal and shear waves preserve waveshape because phase velocity is frequency-independent — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 132; Dispersive media split wave speed into phase and group velocity
• corroborated: 2 independent passages support this claim — David Howard, Jamie Angus, coustics and Psychoacoustics, 105

Broader Connections

• Dispersive media split wave speed into phase and group velocity #expands (0.95)