Other

Dolby Laboratories Licensing Corporation

Lenbrook Industries Limited

Mqa Limited

Meridian Audio Limited

Reinet S.a.r.l.

Craven, Peter Graham

Law, Malcolm

Craven, Peter G.

John Robert Stuart

Peter Graham Craven

Malcolm James Law

Richard J Hollinshead

Alan S J Wood

Michael D Capp

Malcolm Law

Encoding and decoding systems are described for the provision of high quality digital representations of audio signals with particular attention to the correct perceptual rendering of fast transients at modest sample rates. This is achieved by optimising downsampling and upsampling filters to minimise the length of the impulse response while adequately attenuating alias products that have been found perceptually harmful.

Digital encapsulation of audio signals

Methods and devices are described for reducing the audible effect of pre-responses in an audio signal. The pre-responses are effectively delayed by employing a digital non-minimum-phase filter, which includes a zero lying outside the unit circle in its z-transform response. This zero is not paired with another zero at a reciprocal position inside the unit circle, as this would linearise the phase modification. The filtering can introduce a greater group delay at the pre-response frequency than at a low frequency, such as 500 Hz or even 0 Hz. The technique can be used to reduce pre-responses in an existing audio signal and also to pre-empt pre-responses that would be introduced to the audio signal by subsequent processing.

Non linear filter with group delay at pre-response frequency for high res radio

Non linear filter with group delay at pre-response frequency for high res audio

Devices and methods for digital to analog conversion (DAC) are provided, in which the analog outputs of an even number of digital to analog converters are combined. The individual converters operate on the same data but there is a relative time delay between the input digital signal received by one or more of the converters and the input digital signal received by other of the converters, wherein the delay is a fraction of the data sample period. Moreover, the data signal fed to half of the converters has an inverse relationship with the data signal fed to the other half of the converters and their analog outputs are subtracted. Dither and filtering techniques may also be employed.

Digital to analogue conversion

Encoding and decoding systems are described for the provision of high quality digital representations of audio signals with particular attention to the correct perceptual rendering of fast transients at modest sample rates. This is achieved by optimizing downsampling and upsampling filters to minimize the length of the impulse response while adequately attenuating alias products that have been found perceptually harmful.

Methods are provided for equalizing the group delay of a sound reproduction system, in particular a system comprising acoustic transducers with at least one crossover between a lower-frequency and a higher-frequency range. A correction is applied to a signal in the lower-frequency range, including the crossover region, to substantially equalize the group delay for the lower-frequency range, and a signal delay is applied to a signal in the higher-frequency range to bring it into closer alignment with the equalized lower-frequency range signal. The methods may be implemented in the design of an acoustic transducer system and also via a computer program product, which can be implemented as an update or enhancement to an existing digital signal processor loudspeaker system.

Group delay correction in acoustic transducer systems

An encoder for digital audio signals at a higher sample rate creates a stream for consumer distribution at a lower sampling rate, with compatibility for standard PCM players without a decoder. In conjunction with a suitable decoder, two enhanced playback options are supported, the first option allowing full lossless reconstruction of a noise-shaped higher sampling rate signal, the second option allowing lossy bandwidth extension even if an intervening transmission chain has truncated the least-significant-bits of the encoder's output signal.

Doubly compatible lossless audio bandwidth extension

A lossless encoder and decoder are provided for transmitting a multichannel signal on a medium such as DVD-Audio. The encoder accepts additionally a downmix specification and splits the encoded stream into two substreams, such that a two-channel decoder of meagre computational power can implement the downmix specification by decoding one substream, while a multichannel decoder can decode the original multichannel signal losslessly using both substreams. Further features provide for efficient implementation on 24-bit processors, for confirmation of lossless reproduction to the user, and for benign behaviour in the case of downmix specifications that result in overload. The principle is also extended to mixed-rate signals, where for example some input channels are sampled at 48 kHz and some are sampled at 96 kHz.

Matrix improvements to lossless encoding and decoding

In one aspect of the invention, a stream is divided into two substreams, the first substream providing information relating to a 'downmix' signal obtained by matrixing and containing fewer channels than an original multichannel digital signal, and the second substream providing additional information allowing the original multichannel digital signal to be losslessly recovered by a decoder. In a preferred implementation, an encoder furnishes the downmix signal using a cascade of one or more primitive matrix quantizers, each of which implements an n-by-n matrix, followed by selection of the m channels required for the downnix. In a second aspect, a lossless compression system includes a dither seed in the encoded bitstream. The dither seed is used to synchronize a pseudo-random sequence generator in the decoder with a functionally identical generator in an encoder. In a third aspect, encoders and decoders contain uncommitted primitive matrix quantizers, the encoder having logic that accepts a downmix specified as a matrix of coefficients, allocates a number of primitive matrix quantizers to furnish the downmix and optionally allocates a further number to provide matrixing to reduce the data rate.

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Cambridge, United Kingdom

John Robert Stuart