An acoustic [[wave train display]] form. A display mode of the [[acoustic]] [[wave train]] in the [[XZ plane|X-Z plane]] in which the intensity of the photographic beam is modulated with the amplitude of the wave form to produce a variable photographic density pattern as a function of time. All positive half-cycles appear as dark streaks, and all negative cycles which have been cut off appear as light streaks. See [[acoustic log]] and [[variable density]]. Compare amplitude-time or [[XY plane|X-Y plane]]. See illustration at [[wave train display]].