Group delay
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In physics, and in particular in optics, the study of waves and digital signal processing, the term group delay has the following meanings:
1. The rate of change of the total phase shift with respect to angular frequency, d θ/d ω, through a device or transmission medium, where θ is the total phase shift, and ω is the angular frequency equal to 2πf, where f is the frequency.
2. In an optical fiber, the transit time required for optical power, traveling at a given mode's group velocity, to travel a given distance.
Note: For optical fiber dispersion measurement purposes, the quantity of interest is group delay per unit length, which is the reciprocal of the group velocity of a particular mode. The measured group delay of a signal through an optical fiber exhibits a wavelength dependence due to the various dispersion mechanisms present in the fiber.
Source: from Federal Standard 1037C
It is often desirable that group delay be constant across all frequencies; otherwise there is temporal smearing of the signal. Because group delay is -d θ/d ω, as defined in (1), it therefore follows that a constant group delay can be achieved if the transfer function of the device or medium has a linear phase response (i.e., θ = θ0 + Kω where K is a constant).
Thresholds of audibility according to Blauert and Laws:
| Frequency | Threshold |
|---|---|
| 500 Hz | 3.2 ms |
| 1 kHz | 2 ms |
| 2 kHz | 1 ms |
| 4 kHz | 1.5 ms |
| 8 kHz | 2 ms |
See also
External links
- Discussion of Group Delay in Loudspeakers (http://www.trueaudio.com/post_010.htm)