Abstract: A system and method for use in determining the start time of a pressure pulse created by a downhole explosive device detonated by a firing signal includes a downhole tool with a pressure pulse detector that detects the pressure pulse and generates an input signal in response thereto, and a circuit path configured to output a signaling pulse distinguishable from the firing signal. A surface unit receives and discriminates the signaling pulse from the firing signal, and outputs a start time signal in response to receiving the signaling pulse. Alternatively, the downhole tool includes a processor that measures and stores the time that the pressure pulse detector generates the input signal.