A self-cleaning pet litter box has a conveyor to incrementally transport clumped litter material and solid pet waste to a waste receptacle. The wavelength multiplexing processing apparatus includes a waveguide device wherein a plurality of incoming and outgoing waveguides, a first slab waveguide and a plurality of channel waveguides are formed on a substrate, a mirror array device and a lens device. to crystallize as a result of contact with the fluid and adapted to introduce the liquid through one or more outlets into the pipe. In one embodiment, the system minimizes an error function which is computed with the use of two adaptive filters, each such filter being applied to a corresponding one of the two signals received from the given pair of microphones. To compensate for receptor output that may decrease after reaching a peak value during approach of an object, a near condition can be maintained until the change between the two groups of measurements no longer exceeds a different designated value.