Showing papers by "Dolby Laboratories published in 1997"

Method and apparatus for encoding and decoding multiple audio channels at low bit rates using adaptive selection of encoding method

Abstract: A split-band coding system combines multiple channels of input signals into various forms of composite signals and generates spatial-characteristic signals representing soundfield spatial characteristics in a plurality of frequency subbands. The spatial-characteristics signals may be generated in either or both of two forms. In a first form, the signal represents measures of signal levels for subband signals from the input channels. In a second form, the signal represents one or more apparent directions for the soundfield. The type of the spatial-characteristics signal may be adapted dynamically in response to a variety of criteria including input signal characteristics. Temporal smoothing and spectral smoothing of the spatial-characteristics signals may be applied in an encoder. Temporal smoothing and spectral smoothing may be applied to gain factors derived from the spatial-characteristics signals in a decoder.

Audio matrix encoding

Abstract: A surround sound encoder, intended for implementation in software, runs in real time on a personal computer using low mips and a small fraction of available CPU cycles. In the principal application for the encoder, the Lt and Rt signals of the encoder are mixed with the Lt and Rt signals of a pre-recorded source (e.g., computer game soundtrack, CD ROM, Internet audio, etc.). Alternatively, the encoder may be used by itself or with one or more other virtual encoders to provide a totally user-generated soundfield. The encoder is implemented in either of two ways: the signal being encoded may be panned to one or more of the four inputs of a surround-sound fixed matrix encoder or the signal may be encoded by applying the signal to a surround-sound variable-matrix encoder. Phase shifting, required in the encoder, is achieved by applying a signal to two phase-shifting processes, producing two signals whose relative phase difference is sufficiently close to the desired phase shift over at least a substantial part of the frequency band of interest. Satisfactory audible results may be achieved, using very low computer processing power, when one of the phase shifting processes is implemented by a first-order all-pass filter and the other phase shifting process is implemented by only a short time delay, which also has an all-pass characteristic.

Audio system which not only enables the application of the surround system standard to special playback uses but also easily maintains compatibility with a surround system

Abstract: When an audio stream signal is transmitted, the bit stream information for determining the surround mode and special-use mode, including karaoke use, is sensed from the signal at a mode sensor. After the surround mode has been sensed, the audio data is converted by a decoder into a front left, front center, and front right main audio signals and a back left and back right surround audio signals in the surround mode, which are converted into analog signals and outputted to the corresponding speakers. When the special-use mode has been sensed, by using the central main audio signal of the front left, front center, and front right main audio signals and back left and back right surround audio signals converted at the decoder, a normally used first-type accompanying sound selectively made unused, for example, guide melody, is generated. In addition, by using the back left and back right surround audio signals, a normally unused second-type accompanying sound selectively used, for example, vocals, is generated. The first- and second-type accompanying sounds, together with the front left and front right main audio signals, are reproduced selectively. Consequently, a system that transmits surround sound using a plurality of channels can maintain compatibility with a surround system easily, when the plurality of channels are applied to special use, such as karaoke, not being restricted to surround use.

Analysis-/synthesis-filtering system with efficient oddly-stacked singleband filter bank using time-domain aliasing cancellation

Abstract: An efficient implementation of oddly-stacked critically-sampled single sideband analysis/synthesis filter banks is achieved by application of a set of functions to time-domain and frequency-domain values before and after transformation. In one embodiment of an analysis filter bank, a forward pre-transform function groups blocks of N samples into blocks of 1/4N modified samples, a discrete transform generates frequency-domain coefficients in response to the modified samples, and a forward post-transform function generates spectral information in response to the frequency-domain transform coefficients. In one embodiment of a synthesis filter bank, an inverse pre-transform function groups spectral information into blocks of 1/4N frequency-domain transform coefficients, a discrete transform generates blocks of 1/4N time-domain transform coefficients in response to the frequency-domain transform coefficients, and an inverse post-transform function generates blocks of N time-domain samples in response to the time-domain transform coefficients. An implementation of an oddly-stacked Time Domain Aliasing Cancellation transform permits the length of the transformation to be adaptively selected.

Method and apparatus for encoding and decoding audio information representing three-dimensional sound fields

Abstract: 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.

Audio system, reproducing method therefor, recording medium therefor and method for recording on the recording medium

Abstract: PROBLEM TO BE SOLVED: To provide an audio system capable of easily keeping inter-changeability with a surrounding system when it is used in a specific application such as KARAOKE, etc. SOLUTION: When an audio stream signal is transmitted, bit stream information which decides a surrounding mode and a specific application mode such a KARAOKE application, etc., is detected by a mode detector 163. When the surrounding mode is detected, ordinary surrounding reproduction is performed. When the specific application mode is detected, a first type of fundamentally used subordinate voice set as a selectively fundamentally disused one is generated by using a center main audio signal out of left, center and right front main audio signals and left and right rear surrounding audio signals, and a second type of fundamentally disued subordinate voice used selectively by using the left and right rear surrounding audio signals is generated. The first and second types of subordinate voices are reproduced selectively with the main audio signal.

Improvements in Motion Picture Sound: The Academy's New Three-Way Loudspeaker System

Abstract: Digital soundtracks have the capability of delivering lower distortion program signals with flat power bandwidth in the motion picture theater. Traditional two-way theater loudspeaker systems are presently being pushed far beyond their original performance limits with the new soundtracks, and three-way systems are now considered to be their future replacement. The authors have developed such systems for both small and large venues, and an installation of five new screen channels has been made in the Samuel Goldwyn Theater at the Academy of Motion Picture Arts and Sciences. System evolution, design, and performance will be discussed in detail in this paper.