We present a new method for determining the contact time of a rubber ball with the rebounding surface by using a sound-detecting electronic circuit and a digital storage oscilloscope. The rubber ball (a tennis ball or squash ball) is dropped from a known height onto a rigid surface and its contact time on first bounce is determined on the oscilloscope. Using the known value of the coefficient of restitution (COR) of the ball-surface combination, we also determine the value of air pressure inside the ball. (Contains 9 figures.)