The design of spatialization backends depends on the output devices surveyed in the paragraph above. Part of the spatialization process involves processing filter functions (convolution) and reverberation. Such processing can be done either in hardware [Wenzel et al. 90] or software [Intel97]. In the later case the main CPU load might increase unacceptably if the spatial sound design did not anticipate such scalability. Otherwise the software for spatialization disables resource allocation and the acoustical effect cannot be achieved.