1. A quadratic interpolator generating an output signal sample y(x) for each of a plurality of reference values x and based on known signal samples y(-1), y(0), and y(1) spaced apart a predetermined equal amount, x being in a range of one-half of said predetermined equal amount on either side of respective one of said known signal samples, said quadratic interpolator comprising: means for outputting a first signal having value a=y(-1)+y(1)-2y(0) and a second signal having value b=(y(1)-y(-1))/2; and means for inputting x, for determining x.sup.2, for receiving the first signal and the second signal, for producing a third signal having value x times b, for producing a fourth signal having value x.sup.2 times a, and for adding the third signal, the fourth signal and the y(0), and in response generating the output signal sample y(x).