1. A signal processing method using a non-linear transfer function defined by coefficients, k 1 , k 2 , k 3 , and k 4 , and two boundaries, a and b, to produce the output, y, from the input, x, given by y = { ( k 1 + x ) ( k 2 - x ) , x < a x , a ≤ x ≤ b ( x - k 3 ) ( x + k 4 ) , x > b