Abstract
Current practice defines the front velocity of a signal as the limit of the phase velocity for infinitely high frequency. However, the present article provides evidence that the propagation velocities of signal fronts for input signals of nonzero temporal duration result from the phase velocities in the low-frequency range. In conclusion, although the impulse response propagates at the phase velocity for infinitely high frequency, this is shown not to be true for the step response. The article further clarifies that the front or information velocity should be defined as the fastest phase velocity of a transmission medium.