Group delay
= Group delay
{title2=$\tau_g=\partial\phi/\partial\omega$}
The <group delay> is the <frequency> derivative of an unwrapped transfer <wave phase>, using the $e^{-i\omega t}$ convention. It predicts the leading delay of a narrow <wave envelope> when the transfer <wave amplitude> and the delay vary little across its band; it is not generally a signal-front arrival time.