Sri International

Digital Recording Research Limited Partnership

Neural Systems Corp.

Other

Digideck, Inc.

Charles S Weaver

Constance T Chittenden

John M Yarborough, Jr

Joseph H Chadwick

Donald J Burch

Lawrence E Sweeney, Jr

Robert A LeBlanc

A Brit Conner

Allen B Conner, Jr

Constance Dell Chittenden

Floyd A Brown

An error detection and correction apparatus includes three threshold logic units which make decisions based on current and previous bit values in a bit stream of block-coded data. One of the threshold logic units decodes the data stream based on an advancing time stream of data. Another threshold logic unit decodes the data stream based on a time-reversed stream of data, and the last threshold logic unit decodes the data stream based on a time-reversed input stream of data and a time-reversed set of decisions made by the first threshold logic unit. Each threshold logic unit generates decisions and a parity check of those decisions Error identification information is compared between the three streams of decisions and parity checks on those decisions, thereby producing error information, which is processed by a circuit which determines which is the most likely data transmitted.

Error correction apparatus using forward and reverse threshold functions

Apparatus is shown for regenerating a signal stream of binary digits which has been distorted by intersymbol interference during passage through a channel (10 and 12) having insufficient channel bandwidth such that the channel output waveform comprises substantially an analog signal. (FIG. 2 at B and D.) After equalization (24) the channel output is converted to a digital sample signal stream at analog-to-digital converter (26). The converter (26) output is supplied to shift register (28) from which successive groups of digital sample signals produced over a plurality of bit intervals of channel output are shifted to decoder (22). Initialization bits that immediately precede the first group of binary digits to be regenerated also are supplied to decoder (22) through sector header reader (20) for use in decoding the first group of digital sample signals supplied to the decoder. During decoding of subsequent groups of digital sample signals, end bits (3,4 and 5) from the preceding group of regenerated binary digits are supplied to the decoder (22). The decoder includes a plurality of trained networks (40-1 through 40-5 and 50-1 through 50-m) of either the neural network or binary tree type.

Method and apparatus for regenerating a distorted binary signal stream

A binary tree and method of producing a binary tree are shown, together with artificial neural networks which include processing units of binary trees. The binary tree-producing method includes obtaining a set of binary training pattern vectors some of which are associated with a first pattern to be recognized, and the remainder of which are not associated with the first pattern. Those associated with the first pattern and the remainder are identified as category 1 and category 0 vectors, respectively. The set of vectors is used to generate a binary tree in computer memory, which tree includes a sequence of binary doublets each of which represents a tree node. One of four branch conditions is identified by each doublet including no branches, branch only left, branch only right or branch both left and right. The sequence of binary doublets is used to classify binary vectors. A hardware version of the tree may be implemented which includes a plurality of AND gates (1L, 1R, 2L, 2R, 3L and 5L) interconnected in an N-level binary tree (FIG. 3) to which N binary inputs (X.sub.1, X.sub.2 and X.sub.3) are connected to separate levels of the tree. Leaf nodes of the AND gate binary tree are connected to an OR gate (20), and a start signal (S) is supplied to the root node (1) of the tree.

Method for producing a binary tree, pattern recognition and binary

In a digital encoder, truncation is controlled by the fullness of the output rate-smoothing buffer. A signal compression system is shown for processing a stream of fixed length digital sample signals, such as audio signals, which system includes a linear digital compression filter for compression filtering the sample signal stream and generating a stream of compression-filtered signals. The compression-filtered stream is encoded by an encoder which implements a variable word length truncated code. The encoder output is supplied to a buffer for transmission to a communication channel. The encoder is controllably operable in a normal mode and in an out of range (OOR) mode. In the OOR operating mode an OOR code word together with the compression filtered signal is sent to the buffer. Buffer underflow is controlled by operation in the OOR mode when the buffer is empty or near empty. Buffer overflow is controlled by truncating sample signals supplied to the compression filter in response to a measure of buffer fullness when the fullness of the buffer exceeds a predetermined level. The level of truncation increases as buffer fullness increases. With a decrease in buffer fullness, a measure of the rate of change of buffer fullness may be used to accelerate the decrease in truncation for improved audio signal quality. Additionally, a measure of variance of the compression-filtered signal stream may be used in conjunction with control based upon a measure of buffer fullness in the control of truncation for improved audio signal quality.

Data compression system and method with buffer control

Encoding and decoding method and apparatus are disclosed including a decoder for decoding a stream of encoded digital data words which have been encoded by an encoder using variable length code words in which the code words comprise a single group of 0 bits followed by a single group of 1 bits. The 0 bits and 1 bits are separately counted (46), and the combined counts are used to address a read only memory (54) containing the decoded digital data words. The decoded digital data word is read out from the addressed memory location. Also disclosed is an AND gate array 70 of rows and columns of AND gates (90-1 etc.), in which the number of 0s in the code word determines which row is energized, and the number of 1s in the code word determines which column is energized. The energized AND gate is indicative of the decoded digital data word.

Method and apparatus for digital encoding and decoding

Method and apparatus for recurrently obtaining a measure of the systolic slope of the blood pressure wave in a subject's artery during a range of physical activity, or exercise, are disclosed. A plot, or record, of the slope measurements versus heart beat rate, point in an exercise protocol, or the like, is provided from which subjects having coronary artery disease (CAD) may be distinguished from subjects without CAD.

Method and apparatus for diagnosis of coronary artery disease

Audio signals such as ECG, speech and music are digitally processed to reduce the bit-rate needed for accurate transmission, known as minimizing the entropy of the signal. The transmitter features a digital compression filter with zeros restricted to certain points on the unit circle, and Huffman encoding for transmission. The receiver features a digital decompression filter with poles at the zero locations, but shifted inside the unit circle to prevent error-ramp build-up.

Data compression system and method for audio signals

A data reduction system is disclosed which includes an analog to digital converter for converting an analog signal to digital sample signal form, a digital compression filter for compression filtering the digital sample signals, and an encoder for truncated Huffman encoding the compression filter output. A decoder for decoding the encoded signal, a digital reconstruction filter for decomposition filtering of the decoded signal, and digital to analog converter means are included to reconstruct the analog signal. The digital compression filter has a transfer function which includes zeros as the unit circle in the Z-plane, while the digital reconstruction filter has poles that normally are on or inside the unit circle in the Z-plane at the same angular positions as the zeros of the digital compression filter. The poles of the reconstruction filter are momentarily movable inwardly from their normal positions in response to a detected error signal to speed recovery from such error signal.

A music data compression system is disclosed which includes an analog to digital converter for converting the analog music signal to digital sample signal form, a digital compression filter for compression filtering the digital sample signals, and an encoder for truncated Huffman encoding the compression filter output. An entropy setting unit is included in the system for step control of the signal supplied to the digital compression filter in accordance with one or more threshold levels of the envelope of the music signal, and for reducing the entropy of the signal with increases in the energy level of the music signal. Different codes may be implemented in accordance with the threshold(s), and an identifying code word is inserted in the Huffman encoded stream. A decoder, digital reconstruction filter, and digital to analog converter are used to reconstruct the analog music signal. The identifying code word in the encoded signal stream to the decoder is used to select the necessary algorithm for decoding, and an entropy setting unit is included for step control of the gain of the digital reconstruction filter output under control of the identifying code word when step gain control is included prior to compression filtering.

Data compression method and apparatus

Method and apparatus for decoding Huffman encoded words are disclosed which include the use of logic gates connected in the form of a binary decoding tree which includes branches, interior and leaf nodes. Bits of the encoded word are sequentially supplied to gates of the binary tree. Simultaneously, gate enable signals are supplied to gates of the binary tree. Both the data bits and enable signals are supplied to gates at increasingly higher levels of the binary tree. When an output is obtained from a gate associated with one of the leaf nodes of the tree, the process of sequentially supplying data bits and enable signals to gates of the binary tree is repeated for the next encoded word. The original data words are regenerated by use of outputs from said gates associated with leaf nodes of the binary tree.

Method and apparatus for digital Huffman decoding

Digital data compression method and means are disclosed which allow for transmission of digital data over a short time period and/or narrow bandwidth transmission line. Also a maximum amount of information may be stored on a movable recording medium using data compression method of this invention. Digital signals to be stored and/or transmitted first are compressed using a finite-impulse response digital compression filter which generates estimated signal values which are subtracted from actual signal values to provide a sequence of difference signals. The difference signals are encoded using a truncated Huffman type encoding method and means, and the encoded signals are transmitted to a remote receiver and/or are recorded. The receiver includes a decoder and digital reconstruction filter for exact reproduction of transmitted digital signals. The invention is well adapted for storage and/or transmission of three lead electrocardiogram (ECG) signals, recording and playback of music, and the like.

Method and apparatus for digital data compression

Method and apparatus for transferring digital data in a bit stream consisting of digital data words each of which words includes data bits and a parity bit are disclosed. Except for the word parity bits, the stream is transferred without additional overhead bits such as start and stop bits employed in an asynchronous transmission data format or synchronizing characters employed in a synchronous transmission data format. Method and apparatus for locking onto the parity bit of such a bit stream are disclosed which allow for digital data transfer in this format.

Digital data transmission with parity bit word lock-on

A plural channel playback system comprising magnetic recording tape movable past a reproducing transducer head having at least one transducing element for each track is shown together with skew detecting means. At least two of the tracks are recorded with digital data signals comprising equal length data words with a parity bit, with the parity bits being simultaneously recorded along the tracks. Parity bit lock-on circuits are responsive to outputs from two tracks, which lock-on circuits generate word clock pulses in synchronization with the recorded parity bit signals. A phase detector responsive to word clock pulses from the parity bit lock-on circuits produces an error signal output proportional to the phase difference between said word clock pulse inputs thereto, which error signal is related to skew. The azimuthal position of the reproducing head relative to the recording tape is adjusted either manually or automatically to minimize the error signal.

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Palo Alto, CA, United States of America

Charles S Weaver