Can somebody interpret "group delay" for me??

I'm confused.
thx a lot.

Hi,

The group delay for a signal passing through a filter is the among of time needed to all the frequencies of this signal to pass the filter. For example if the signal at the input of a filter is a pulse and if the group delay is not constant for all frenquencies, at the output of the filter the signal will be distorded and not look like the initial pulse. The phase response of the filter is not the same for all frequencies, so the group delay of each frequency is different.

and more precisely we can say that,

1. The rate of change of the total phase shift with respect to angular frequency, dΘ /dω , 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.


Reference:

https://www.its.bldrdoc.gov/fs-1037/dir-017/_2508.htm

ths
But how can I calculate the total phase shift or total time for all frequecies of the signal?