# Homework Help: Group delay of LTI system

1. Nov 19, 2011

### ElfenKiller

1. The problem statement, all variables and given/known data

Show that the group delay of an LTI discrete-time system characterized by a frequency response $H(e^{j\omega})$ can be expressed as

$\tau(\omega)= Re\left\{\frac{j\frac{dH(e^{j\omega}}{d\omega}}{H(e^{j\omega}}\right\}$.

2. Relevant equations

3. The attempt at a solution

I think I understand the rest of the proof (not shown here) but I don't see why the equation in (2) is valid. First, I had the idea that the first term in the equation in (2) is the real part and the second term in the equation is the imaginary part of the derivative, but it does not really appear to me to be like that.

Last edited: Nov 19, 2011
2. Nov 21, 2011

### ElfenKiller

Found the solution by asking some friend. If someone wants to know it, let me know.