Abstract: An adaptive high-fidelity perceptual subband encoder for spatially directional multichannel audio signals, using a mixture of individual-channel subband coding with subband-steered composite-channel signal coding that combines the spectral components of the individual channel subbands selected for steering. The composite channel representation includes a subband steering control signal which either conveys the levels of the spectral components from all the steered channels, or represents the apparent directions (net directional vectors) of the spectral components from all the steered channels.

Abstract: The invention relates in general to low bit-rate encoding and decoding of information such as audio information. More particularly, the invention relates to computationally efficient adaptive bit allocation and quantization of encoded information useful in high-quality low bit-rate coding systems.In one embodiment, an audio split-band encoder splits an input signal into frequency subband signals, quantizes the subband signals according to values established by an allocation function, and assembles the quantized subband signals into an encoded signal. The allocation function establishes allocation values in accordance with psychoacoustic principles based upon a masking threshold.

Abstract: Two or more audio channels (i.e.--stereo, 4-channel surround, etc.) are each divided into frequency subbands to be coarsely quantized. An adaptive bit allocation scheme is then applied to subbands which are combined across channels such that equivalent subbands (i.e.--same frequency band) from each channel are grouped together to form a steered subband. The power from each subband is averaged across the channels to form a steered subband level. Bits are conserved by forming a vector in which each channel is represented by the difference between the steered subband level (average) and the actual subband level. Subbands which are not steered are represented by the coarse quantization and are considered unsteered channel subbands. Subbands which are steered are represented by vectors and are considered composite channel subbands. Vectors may be represented using a lookup table and the steered subband levels may be calculated using alternatives such as a peak level rather than an average.

Abstract: A split-band encoder prepares an estimate of an input signal spectral envelope by splitting the input signal into frequency subband signals, generates a scaled representation of the subband signals comprising scaling factors and scaled values, generates a differential coded representation of the scaling factors, and assembles the differential coded representation and scaled values into an encoded signal. The scale factors represent a spectral envelope of the input signal and spectral leakage between filterbank subbands limits the change in value between adjacent scaling factors. This limitation in change can be exploited to reduce the informational requirements of the differential coded representation. Adaptive selection between high- and low-resolution spectral envelopes and adaptive scaling factor reuse are described.

Abstract: An apparatus or method which applies data compression techniques such as multi-dimensional Huffman encoding uses compact encoding tables which are smaller than conventional tables by ordering symbols within messages prior to coding and passing order information with the resulting code word. An apparatus or method which applies data decompression recovers a message from a compact decoding table in response to a code word and reorders symbols within the message according to order information received with the code word.

Abstract: The invention relates in general to low bit-rate encoding and decoding of information such as audio information. More particularly, the invention relates to the suppression of quantizing noise which results from low bit-rate encoding and decoding of signal events such as transients. An encoder identifies intervals of an input signal in which a decoder is likely to generate audible artifacts caused by quantizing errors. Indications of these intervals are passed in the encoded signal to the decoder. The decoder uses these indications to eliminate quantizing artifacts by suppressing corresponding intervals in the output signal.

Abstract: The invention relates in general to the quantization of digital signal information. More particularly, the invention relates to the reduction of perceptible effects of quantizing noise by reserving a special quantizing level for low-level signals in encoding and decoding applications.

Abstract: The invention relates to the reproduction of high-fidelity multi-dimensional sound fields intended for human hearing. More particularly, the invention relates to the decoding of signals representing such sound fields delivered by one or more delivery channels, but played back over a number of presentation channels which may differ from the number of delivery channels. In one embodiment, a subband decoder combines spectral information in the frequency domain prior to inverse filtering, thereby incurring implementation costs roughly proportional to the number of presentation channels rather than to the number of delivery channels.

Abstract: A method and apparatus for transmitting a digitally modulated Quadrature Phase Keyed (QPSK) audio carrier signal, or a digitally modulated Quadrature Partial Response System (QPRS) audio carrier signal, wherein the audio carrier signal is located 1.2 MHz below the video carrier of an NTSC signal. This places the digital audio signal 300 KHz above the analog FM sound center frequency of the NTSC signal in the adjacent lower channel, 4.8 MHz above the video carrier of the adjacent lower channel NTSC signal and at the edge of the lower vestigal video sideband components of the NTSC signal with which the digital audio signal is associated.

Abstract: The invention relates to the reproduction of high-fidelity multi-dimensional sound fields intended for human hearing. More particularly, the invention relates to the decoding of signals representing such sound fields delivered by one or more delivery channels, but played back over a number of presentation channels which may differ from the number of delivery channels. In a preferred embodiment, a decoder implemented by a discrete digital inverse transform incurs implementation costs roughly proportional to the number of presentation channels.

Abstract: The decoder of this invention decodes at least two channel signals in a directional information system where one or more input signals containing directional information have been encoded into the two or more channel signals. The decoder generates a first control signal substantially proportional to the logarithm of the ratio of the amplitudes of two of the channel signals to detect, as between two of the channel signals, whether the amplitude of one signal dominates that of the other. The decoder also generates a second control signal substantially proportional to the logarithm of the ratio of the amplitudes of the sum and the difference between two of the channel signals to detect the dominant signal in terms of amplitude. The decoder includes a matrix means responsive to the two or more channel signals and the two control signals for generating a number of output signals according to an algorithm.

Abstract: The decoder of this invention decodes at least two channel signals in a directional information system where at least four input signals containing directional information have been encoded into the two or more channel signals. The decoder generates a first control signal substantially proportional to the logarithm of the ratio of the amplitudes of two of the channel signals to detect, as between two of the channel signals, whether the amplitude of one signal dominates that of the other. The decoder also generates a second control signal substantially proportional to the logarithm of the ratio of the amplitudes of the sum and the difference between two of the channel signals to detect the dominant signal in terms of amplitude. The decoder includes a matrix means responsive to the two or more channel signals and the two control signals for generating a number of output signals according to an algorithm.

Abstract: The decoder of this invention decodes at least two channel signals in a directional information system where at least four input signals containing directional information have been encoded into the two or more channel signals. The decoder generates a first control signal substantially proportional to the logarithm of the ratio of the amplitudes of two of the channel signals to detect, as between two of the channel signals, whether the amplitude of one signal dominates that of the other. The decoder also generates a second control signal substantially proportional to the logarithm of the ratio of the amplitudes of the sum and the difference between two of the channel signals to detect the dominant signal in terms of amplitude. The decoder includes a matrix means responsive to the two or more channel signals and the two control signals for generating a number of output signals according to an algorithm.

Abstract: The complementary pre-processing and post-processing circuits of this inventiona re advantageous for reducing noise introduced into a signal by a process or medium where the noise introduced rises with the signal level. The pre-processing circuit analyzes the spectral composition of an input signal and generates an emphasis control signal to so indicate. The emphasis control signal is limited by a limitation circuit to a desired bandwidth. The pre-processing circuit includes an emphasis applying circuit for amplifying or attenuating the input signal as a function of the emphasis control signal. A delay circuit delays the input signal relative to the emphasis control signal so that the input signal reaches the emphasis applying circuit when the emphasis control signal is available for controlling the amplification or attenuation applied.The post-processing circuit restores the spectral composition of the signal.

Abstract: An encoder converts an analog input signal to a digital signal. The encoder comprises a circuit for generating a control signal with a predetermined bandwidth from the input analog signal. The control signal indicates the desired optimum step-size to be applied in the encoder. The encoder further comprises a converter for converting the analog input signal to a digital signal. The converter is responsive to the control signal representing step-size so that the digital signal will be generated in accordance with the step-size information. Since the generation of a limited bandwidth control signal requires time, the encoder also includes a circuit for introducing time delay to the analog input signal, so that the delayed input signal reaches the converter when the control signal is available for digital encoding.A decoder generates an analog output signal from a digital signal received from an encoder through a transmission medium.

Abstract: The error concealment system of the invention is for use with a delta modulation or delta signal modulation decoder which decodes digital signals received through a transmission or storage medium from an encoder. The encoder groups the digital signals into a plurality of blocks of one bit words. The decoder also receives from the encoder information related to the number of 1's in each of the blocks of one bit words before transmission or storage. The system comprises means for deriving information on the number of 1's in each received block of words and for comparing such information to the information received from the encoder to determine the presence and polarity of any bit errors. The system further includes means for introducing into each received block determined to contain one or more errors at least one bit error of the opposite polarity from that determined to conceal at least some of the effects of the bit errors.

Abstract: Discrete four-channel photographic (optical) motion picture sound-tracks are disclosed that are compatible with existing monophonic and stereo variable area (SVA) theatre projection equipment. Six track and four track embodiments are disclosed. In the four track embodiments 4-4-4 matrix encoding is employed in producing the sound-track. Apparatus for recording and reproducing the compatible four-channel sound-tracks are also disclosed.

Abstract: This invention reduces crosstalk interference components without a significant increase in recorded bandwidth of the modulated audio signals and without a significant degradation of the signal-to-noise ratio of the reproduced audio signals. According to the invention, the nominal carrier frequency of the modulated audio signals in adjacent tracks or scans is offset by an amount sufficient to shift the crosstalk interference components outside the desired audio pass band for substantially all modulating amplitudes and frequencies. At the same time, the modulated audio frequency spectra of the adjacent tracks substantially overlap so that additional overall bandwidth requirements are minimized. A satisfactory offset from track to track is in the order of twice the maximum audio response frequency. As the offset is reduced or as occasional high frequency high amplitude audio occurs in adjacent tracks, crosstalk distortion components will tend to appear beginning at the high frequencies.