Other

Dolby Laboratories Corporation

Dolby Laboratories Licensing Corporation

Sony Corporation

Ray M Dolby

Mark Franklin Davis

Craig C Todd

Kenzo Akagiri

Ioan R Allen

Stanley G Cossette

Paul Anthony Spencer

Randolph G Pauker

A spatial audio coding system, including an encoder and a decoder, operates at very low bit-rates and is useful for audio via the Internet. The listener or listeners preferably are located within a predictable listening area, for example, users of a personal computer or television viewers. An encoder produces a composite audio-information signal representing the soundfield to be reproduced and a directional vector or 'steering control signal.' The composite audio-information signal has its frequency spectrum broken into a number of subbands, preferably commensurate with the critical bands of the human ear. The steering control signal has a component relating to the dominant direction of the soundfield in each of the subbands. Because the system is based on the premise that only sound from a single direction is heard at any instant, the decoder need not apply a signal to more than two sound transducers at any instant.

Low bit-rate spatial coding method and system

In an encoder, multiple channels of audio information representing multidimensional sound fields are split into subband signals and the subband signals in one or more subbands are combined to form composite signals. The composite signals, the subband signals not combined into a composite signal and information describing the spectral levels of subband signals combined into composite signals are assembled into an encoded output signal. The spectral level information conveys either the amplitude or power of the combined subband signals or the apparent direction of the sound field represented by the combined subband signals. In digital implementations, adaptive bit allocation may be used to reduce the informational requirements of the encoded signal.

Method and apparatus for encoding and decoding audio information

Two-stage compression and expansion of coupling processed multi-channel

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.

Encoder/decoder for multidimensional sound fields

Three related embodiments of audio signal dynamic range circuits for consumer and semi-professional audio signal compressors, expanders, and compressor/expander noise reduction systems incorporate certain basic features of professional Spectral Recording (SR) while adapting SR for use with consumer recording media (particularly audio cassette tape) and reducing the cost and complexity of the SR circuitry. In addition, the three embodiments, and particularly the preferred embodiment, provide substantial compatibility with the existing B-type and C-type consumer and semi-professional noise reduction systems. Subjective performance substantially equivalent to 16-bit PCM audio systems is achieved with analog audio cassette tape media. In all three embodiments there are two cascaded stages: (1) a high-level stage having a high-frequency fixed-band/sliding band action-substitution sub-state and a low-frequency fixed-band sub-stage and (2) a low-level stage having only a high-frequency fixed-band/sliding band action-substitution sub-stage. The dynamic action regions of the high-frequency action-substitution sub-stages are staggered. Each of the high-frequency sub-stages provides up to 12 dB of dynamic action (together providing up to 24 dB of dynamic action) and operates in a frequency band defined by a single-pole filter having a high-pass shelving response with a corner frequency of 400 Hz. The low-frequency sub-stage provides up to 10 dB of dynamic action and operates in a frequency band defined by a single-pole filter having a low-pass shelving response with a corner frequency of 200 Hz. The single-pole filter characteristics provide a broad and smooth overlap of the high-frequency and low-frequency characteristics. Particular forms of spectral skewing and antisaturation enhance the performance of the circuits with consumer recording media.

Audio compressor, expander, and noise reduction circuits for consumer

Means for reducing the effects of vertical perturbations of a phonograph disc surface resulting from disc and/or playback system mechanical imperfections. Such imperfections are compensated by closed loop and/or open loop means wherein the deviations of the record path are detected and employed to minimize the effects of the mechanical imperfections.

Disc reproducing system for compensating mechanical imperfections

In circuits for generating rapidly changing, yet smooth and controlled, control signals in response to transient signals for use in audio compressors and expanders, a steady-state portion of the control circuit includes first and second smoothing stages (alternatively, a single stage may be employed) and an overshoot suppression portion of the control circuit rapidly charges the capacitor in the steady-state smoothing stage from which the control voltage is derived. A first additional overshoot suppression circuit provides further charging of the capacitor in response to low frequency signal components. Modulation control signals, which make the compressor or expander less susceptible to control by stop-band signal components, are combined in opposition to the signals in the steady-state and overshoot suppression portions of the control circuit. A further overshoot suppression circuit provides additional charging of the capacitor in order to compensate in certain cases for the use of modulation control signals.

Transient control aspects of circuit arrangements for altering the

A 'hybrid' encoder has a characteristic action suitable for substantially full complementary playback in an audio signal transmission or recording system using decoders designed for one type complementary encode/decode system while permitting compatible decoding with decoders designed for use with another type complementary encode/decode system, or playback without any special decoders at all. The hybrid encoder is a series or parallel arrangement of two encoders that are modifications of standard encoders used in the two systems. In the preferred embodiments the two systems are A-type noise reduction and spectral recording. A variable degree of hybrid encoding is provided by varying the characteristic controlling circuit parameters in the two encoders, or in a preferred embodiment, by providing a variable combining arrangement that selects selects from the outputs of a hybrid encoder and an unmodified encoder (spectral recording).

Audio encoder for use with more than one decoder each having different

Circuits for modifying the dynamic range of signals, particularly compressors and expanders for use in noise reduction compander systems, in which the advantages of fixed band characteristics (variable attenuation throughout all or part of the frequency band) and sliding band characteristics (variable attenuation through part of the frequency band achieved by a variable pass filter) are provided, without the disadvantages normally inherent in each characteristic. The outputs of fixed band and sliding band circuit elements variably selected by a combining means operated by a control circuit which senses signal frequencies and/or levels, the elements operating in generally the same level range and at least a partial overlapping in frequency range.

Circuit arrangements for modifying dynamic range using variable

When impedance elements such as FETs are used in attenuators, the elements have linear responses only when the signals attenuated are below certain signal levels. When signal conditions causing the element to operate non-linearly are detected, bootstrapping is applied to reduce the voltage across the element so that the element will operate linearly. The control signal at the gate of the element is then modified to compensate for the increase in effective impedance of the element caused by bootstrapping. The improved attentuators are especially useful in signal compressors and expanders.

Attenuator circuit employing bootstrapping

An audibly distinctive test signal, a pink noise signal at a standard level and periodic but brief interruptions (optimized for the ear's memory for level and spectral differences), is applied to a recording medium or transmission channel. The test signal recovered from the recording medium or transmission channel is compared and matched to a reference uninterrupted pink noise signal at a standard level, the interruptions being used to switch between the test and reference signals and to provide an audible cue as to the identity of the signal heard at any moment so that a rapid confirmation and adjustment, if necessary, of recording/reproduction or transmission/reception calibration can be achieved primarily by ear and, if desired, also by applying the signals to measuring instruments.

Apparatus and method for calibrating recording and transmission systems

The drain-source conductance of a wide variety of FETs can be made to conform to a predetermined function of a control signal. The control signal is multiplied by a factor and an offset is added or subtracted therefrom to derive a modified control signal. The modified control signal is then applied to the gate of a FET. The factor and the offset are such that the drain-source conductance of the transistor is substantially the predetermined function of the control signal. When a desired attenuator characteristic defined with respect to a FET is to be provided using a FET having characteristics different from those of the reference FET, the control signal to the FET used can be similarly modified so that the desired attenuator characteristics are obtained. A dual path compressor or expander employing an attenuator (which includes a FET) in its further path can be made to conform to a desired compression or expansion characteristic defined with respect to a similar arrangement and with respect to a reference FET conductance control characteristic. This can be accomplished by making the conductance control characteristics of the FET to be used to conform to the desired conductance control characteristic.

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San Francisco, CA, United States of America

Ray M Dolby