Embodiments herein discuss tuning a testing apparatus to better match the input response of a target system in which a cable will be used. For example, conductors in the cable may have a different skew depending on the system in which they are used. The testing apparatus may be tuned using frequency information regarding the type of signals that will be driven on the cable when installed in the target system. In one embodiment, the testing apparatus adjusts a testing cycle refresh rate for generating a testing signal which changes the frequency content of the testing signal. Using the adjusted testing cycle refresh rate results in the driver outputting a testing signal that better reflects the actual signals that will be transmitted on the cable in the target system.