1. On a sensory reproduction system having a processor with an instruction set including at least a computationally expensive floating point power function and a set of computationally less expensive floating point operations, a method of efficiently converting sensory data between a perceptual data representation and a physical data representation, where the perceptual data representation is related to the physical data representation by an expression involving a power function, the method comprising: performing a plurality of the computationally less expensive floating point operations on an item of the sensory data; combining results of the plural performed operations to yield an approximation of a result of the power function on the sensory data item; and evaluating the expression using the approximation to provide a converted sensory data item.