Adaptive digital coder and decoder

A method of decoding a coded digital information signal transmitted from a first to a second location over a digital transmission facility operating at a second bit rate, said digital information signal having priorly been converted from an analog information signal using delta modulation at a first bit rate substantially higher than said second bit rate, said coded signal comprising a digital signal representative of information and interspersed coded bit patterns representative of momentary interruptions in said information with the coded bit patterns having idealized correlation properties and also indicating in which range the length of the momentary interruption interval falls, selected from predetermined ranges of unequal length which increase in a nonlinear manner, which comprises the steps of:

• buffering the digital signal and coded bit patterns received from the output of said digital transmission facility at said second bit rate;
• forwarding the buffered digital signal at said first bit rate to a digital-to-analog converter;
• monitoring the output of said digital transmission facility to detect the presence of said coded bit pattern;
• interrupting the transfer of digital signals into said digital-to-analog converter each time that a coded bit pattern is so detected;
• generating an idle bit pattern having a number of bits within the range determined by the information contained in the coded bit patterns detected in said monitoring step;
• forwarding said idle bit pattern to said converter while said digital signal transfer remains interrupted;
• restarting the flow of digital signals to said digital-to-analog converter until the next coded bit pattern is detected;
• and
• reconverting, in said digital-to-analog converter, the digital signal and interspersed idle bit patterns into said analog signal.

Apparatus for transmitting an analog information signal from a first to a second location which comprises:

• a. at said first location:
• means for converting said analog information signal into a digital information signal at a first bit rate using delta modulation;
• means, responsive to each momentary interruption in the information content of said analog signal which exceeds a predetermined interval, for generating at least one coded bit pattern which is representative of the digital signal output from said converting means during said momentary interruption with the coded bit patterns having idealized correlation properties and also indicating in which range the length of the momentary interruption interval falls, selected from predetermined ranges of unequal length which increase in a nonlinear manner;
• means for substituting said coded bit pattern for the digital signal output from said converting means during said momentary interruption;
• and
• means for transmitting said digital signal and interspersed coded bit pattern to said second location at a second bit rate which is substantially less than said first bit rate;
• and
• b. at said second location:
• means, responsive to the output of said transmitting means, for detecting said coded bit patterns and generating a bit sequence substantially corresponding to the digital signal output from the converting means at said first location during said momentary interruption;
• means, connected to the output of said transmitting means, for converting said digital signal back into said analog signal, said converting means operating at said first bit rate;
• and
• means, responsive to the output of said detecting means for temporarily halting the transfer of digital information from said transmitting means to said converting means whenever a coded bit pattern is detected and substituting therefor the bit sequence generated by said detecting means, whereby said analog information signal is recreated at said second location with substantially total fidelity.

An adaptive encoder which comprises:

• means for receiving a delta modulated digital input signal, at a first bit rate, which is representative of an analog information signal of a type that includes occasional but randomly spaced intervals of substantially zero information content;
• means, connected to said receiving means, for detecting a bit pattern in said digital input signal representative of a zero information content interval exceeding a predetermined interval;
• a first, "first-in, first-out", buffer connected to said receiving means for storing said digital input signal;
• means, responsive to said detecting means, for interrupting the flow of binary information from said receiving means to said first buffer each time that said detecting means detects a bit pattern representing a zero information content of the original analog signal;
• means, responsive to the output of said detecting means, for generating at least one coded bit pattern which is representative of the zero information content bit pattern which the coded bit patterns having idealized correlation properties and also indicating in which range the length of the zero information content interval falls, selected from predetermined ranges of unequal length which increase in a nonlinear manner;
• means for feeding said at least one coded bit pattern to said first buffer while the flow of binary information from said receiving means is interrupted;
• means for restarting said flow of binary information after said at least one coded bit pattern has been stored in said first buffer;
• and
• means for reading-out the digital input signal and interspersed coded bit patterns stored in said first buffer at a second bit rate which is substantially less than said first bit rate.

An adaptive decoder which comprises:

• means for receiving a digital input signal, at a second bit rate, said input signal comprising a digital signal which is a delta modulation representation of an analog information signal of a type that includes occasional but randomly spaced intervals of substantially zero information content, the portions of said digital signal representative of said zero information content intervals having priorly been replaced by at least one coded bit pattern if they exceed a predetermined threshold length with the coded bit patterns having idealized correlation properties and also indicating in which range the length of the zero information content interval falls, selected from predetermined ranges of unequal length which increase in a nonlinear manner;
• a first, "first-in, first-out-38 buffer connected to said receiving means for storing said digital input signal;
• means, connected to the output of said first buffer, for detecting said at lease one coded bit pattern;
• means, connected to said detecting means, for forwarding said digital input signal at a first bit rate to a digital-to-analog converter for conversion to said analog information signal;
• means, responsive to said detecting means, for interrupting the flow of the digital input signal to said forwarding means each time that a coded bit pattern is detected;
• means, connected to said forwarding means, for generating a bit stream substantially representative of the zero information content represented by said at least one coded bit pattern for transmission to said digital-to-analog converter, while the flow of said input signal remains interrupted;
• and
• means for restarting the flow of the digital input signal to said forwarding means after said bit stream has been transmitted.