what is the frequency response?
Frequency response is $1/(1−ce^{iw})$, if you want to get amplitude information you just need to get the magnitude of this complex function and its phase will be the inverse of the phase of $1/(1−ce^{iw})$ or 

$$-\arctan (-c\sin w/(1-c\cos w))$$

You can compute the magnitude of the transfer function by:

$$ 1 / sqrt( (-c\sin w)^2 + (1-c\cos w)^2 )$$