The effects of mechanical and electrical filtering were examined for signals obtained from a strain gauge installed at a dart of an impact tester, Mechanical filtering was provided by placing a thin rubber sheet on the impacted surface of the specimens, The electrical filtering was done using a 3 kHz low-pass filtering circuit in the strain amplifier. It was shown from tile results for polycarbonate Charpy specimens that mechanical filtering with a thickness of 0.5 and 1.0 mm gives good reliability for the impact velocity at both 2.8 and 4.0 m/s, not only in reducing the inertial oscillation effect but also in correctly providing values of impact energy.