A folding unit for corrugated cardboard sheets in inline production of corrugated cardboard boxes, comprising a pair of parallel and laterally displaceable folding beams each with an endless conveying belt, which folding beams extend from the inlet of the folding unit to a pair of rolls at the outlet of the folding unit. A lens controls light, emitted by LEDs, that is used to irradiate a photosensitive drum. The earphone further includes an adjusting element for adjusting the position of the mounting element with respect to the body of the earphone. The frame and the platform are relatively disposed such that when the frame lifts a vessel above the surface of the body of water it also lifts the platform above the surface of the body of water. Signal masking functions whose amplitudes are below the amplitudes of their frequency neighbors are nulled.