When transmitting frequencies in a quadripole, the phase position of the frequencies among each other plays an important role in addition to the frequency response. The phase positions of a frequency group are called group delay. It would be ideal if the phase delays were independent of frequency.
The phase positions of frequencies depend on the frequency-determining components or circuits: on capacitances, inductances, cables, oscillating circuits and filters. Since in a frequency-influencing quadripole lower frequencies behave differently than higher frequencies in their phase position and thus the propagation time, the phase relation of the frequencies to each other, the group delay, is a criterion for the transmission behavior of the quadripole. A quadripole with strong group delay changes will therefore transmit non-sinusoidal signals distorted, because the harmonics have different propagation times in the quadripole.
Independent of the frequency range, the group delay influences the sound image in the audio range as well as the transmission characteristics of radio links or RF amplifiers. Group delay times lead to signal distortions which may prevent the information content of a message from being recognized.