Forward-adaptive delta modulator without explicit transmission of step size

The paper deals with an investigation that was carried out to determine whether a forward-adaptive delta modulator without explicit step- -size transmission could he applied successfully to the digital encoding of speech signals at low sampling rates. It was hypothesized that the quality of reproduced speech for the forward- -adaptive delta coder without explicit step-size transmission would be better than that of the conventional backward- -adaptive delta modulator at the same sampling frequency. The first results of the experimental investigation show that although the reproduced speech is reasonably intelligible, it is very difficult to ensure that the tracking between the compressor at the transmitter and the expander at the receiver is very close over a large dynamic range of the input signal.