The rate of change of phase of the response of a device or a system as a function of frequency. A pure time delay, equal at all frequencies, gives a constant slope ofphase versus frequency. If, in an audio component (frequently a passive network), this slope is not constant but varies with frequency, the component is said to produce group delay distortion. This is equivalent to a time delay that varies with frequency, called a group delay because the distortion occurs within a group of adjacent frequencies, but not over the entire spectrum. The audible result is a loss of precision in musical transients; they are spread out or smeared in time and a more diffuse stereo image results.