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