Adaptive digital coder and decoder

Claim 5

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.

Claim 6

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.

Claim 7

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.

Claim 8

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.

Claim 9

The encoder according to claim 4 further comprising: a second buffer connected between said receiving means and the input to said first buffer, said second buffer having a bit capacity corresponding to said predetermined interval of the duration of said zero information content bit pattern, comprising several samples of the analog information.

Claim 10

The encoder according to claim 4 further comprising: means, responsive to the output of said detecting means, for counting the number of bits in said zero information content bit pattern, and said coded bit pattern generating means comprising: means for storing a plurality of coded bit patterns each having idealized correlation properties; means, responsive to the count determined by said counting means, for selecting a particular sequence of said coded bit patterns; and wherein said detecting means includes means to convert the digital signal to the original analog signal and monitors the resulting analog signal for being within a given threshold value from the zero level to determine said zero information content.

Claim 11

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.

Claim 12

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.

Claim 13

The decoder according to claim 7 wherein said detecting means comprises: a second, n-stage, "first-in, first-out" buffer interposed between said first buffer and said digital-to-analog converter; and a correlation detector having inputs connected to each stage of said n-stage second buffer.

Claim 14

The decoder according to claim 8 wherein each of said coded bit patterns is n bits long and has idealized correlation properties, and said n-stage, second buffer includes means for detecting said coded bit pattern and advancing said buffer in steps of n bits to detect up to four sequentially received n-bit encoded bit patterns.

Claim 15

The decoder according to claim 8 wherein each of said coded bit patterns is n/4 bits long, has idealized correlation properties, and said n-stage second buffer can detect up to four of said coded bit patterns accumulated in the n-bit buffer.

Claim 16

The decoder according to claim 8 wherein said bit stream generating means comprises: a logic circuit connected to said correlation detector for determining the duration of said zero information content bit stream; a bit generator responsive to said logic circuit for generating a continuous train of binary digits of the predetermined zero information pattern; and a bit counter connected to the output of said bit generator and to said logic circuit for interrupting the output of said bit generator when said bit stream has attained the desired duration.

Claim 17

The decoder according to claim 11 including a logic circuit wherein said determination of the duration of said zero information content bit stream is adaptively dependent on the number of the information bits being buffered in the decoder at a given instant, such that said durations of zero information content bit stream is lengthened in a predetermined way if said number of stored information bits is low, and shortened if said number is high.