Code converting system and method for band compression of digital signals

Abstract

A code converting system for converting a digital signal having a given number of bits into a digital signal having a different number of bits, which selectively alters the encoding method depending on the nature of the input to the system. The system includes a variable length encoder; a run-length encoder; a multiplexer for selecting as its output either the variable length code or the run-length code; a buffer memory for receiving and storing the output of the multiplexer, supplying it to a transmission line, and generating a signal indicative of the level of memory occupancy of the buffer memory; and control means for controlling the multiplexer so as to output only variable length code when the memory occupancy is below a first predetermined level. The control means further comprises an underflow signal generator for generating a signal indicative of when the memory occupancy is less than the first predetermined level. The underflow signal is supplied to a gate, which transfers it as a selection signal to control the multiplexer so as to output only said variable length code when such underflow occurs. In the absence of an underflow indication signal, the gate is enabled to pass the input code, to the run-length encoder to be converted into a run-length code. The control means is also adjustable so as to control the level of memory occupancy of the buffer memory.