In short, the term Group Delay is used to refer to the average time delay imposed over the range of frequencies the filter is designed to pass through.
The term comes from considering a ‘group’ of signal frequencies.
In fact, one can always expect signals to take a finite time to propagate through any circuit or element in a system. Hence Group Delay values can also be quoted for amplifiers, transistors, or even cables.
mendenz,
Group delay is defined as the derivative of phase with respect to frequency. If a filter has constant group delay over a range of frequencies, then waveforms containing only that range of frequencies will all be delayed by a fixed amount, equal to the group delay, and will be undistorted. There is another parameter called "phase delay" which is defined as phase divided by frequency at a fixed frequency.
Regards,
Kral
This term is very important, because if the group of frequencies that compose the signal, phase distortion occours. It is like the light thue a cristal it decompouses in his components of light. The same occour some frecuencies appear first then other and so on. But all frecuencie components arrives at the same time.