a) A signal defect caused by different frequencies having differing propagation delays. b) This distortion is present when signal components of different frequencies experience different delays as they pass through a system. Distortions are expressed in units of time. The largest difference in delay between a reference low frequency and the other frequencies tested is typically quoted as the group delay distortion. Group delay problems can cause a lack of vertical line sharpness due to luminance pulse ringing, overshoot, or undershoot. The Multipulse or (Sin x)/x signals can be used to check for group delay in the same way as these signals are used to check for chrominance to luminance delays.