A Class of Companded Unity Bit Coders

Speech encoding using unity bit coders in the form of delta modulators (DM) has become very popular. Many different designs have been proposed and implemented in monolithic form. The strategy used in all of these coders is to adapt the `step size´ of the coder to suit the input signal power. The author examines a class of unity bit coders where a basic linear coder is used while the input to this coder is constrained or compressed to be within suitable limits, so as to have the linear coder operating in its optimal range. Results are presented for delta modulators, delta-sigma modulators, and a modified unit bit coder, and it is found that some of the coders perform as well as the `conventional´ adaptive delta modulators.