1. A method for speech coding comprising the steps of: digitizing an input speech signal; detecting active voice and background noise segments within the digitized input speech signal; determining linear prediction coefficients (LPC) and an LPC residual signal of the digitized input speech signal; determining a pitch prediction contribution from the linear prediction coefficients and the digitized input speech signal according to an analysis-by-synthesis method when an active voice speech segment is detected; and determining a pitch prediction contribution from the linear prediction coefficients and the digitized input speech signal using an adaptive code book contribution as a source of a pseudo-random sequence whenever a background noise segment is detected.