This paper proposes a technique for characterization of the frequency-dependent losses in a wireline communications link. By using the measured jitter at the output of a receiver front-end as its only input, this method is able to estimate both the pulse response and frequency response of the link, including the effects of the transmitter output, the channel itself, and the receiver front-end. Simulated and measured results verify the accuracy of this technique, which can be used to efficiently adapt the settings of critical circuit blocks in the link, such as equalizer tap weights.