Patent
1992-09-04
1996-12-10
Knepper, David D.
395 239, 395 214, G10L 918, G10L 700
Patent
active
055839622
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates in general to the recording, transmitting, and reproducing of multi-dimensional sound fields intended for human hearing. More particularly, the invention relates to the high-fidelity encoding and decoding of signals representing such sound fields, wherein the encoded signals may be carried by a composite audio-information signal and a steering control signal.
BACKGROUND ART
A. Goal of High-Fidelity Reproduction
A goal for high-fidelity reproduction of recorded or transmitted sounds is the presentation at another time or location a faithful representation of an "original" sound field. A sound field is defined as a collection of sound pressures which are a function of time and space. Thus, high-fidelity reproduction attempts to recreate the acoustic pressures which existed in the original sound field in a region about a listener.
Ideally, differences between the original sound field and the reproduced sound field are inaudible, or if not inaudible at least relatively unnoticeable to most listeners. Two general measures of fidelity are "sound quality" and "sound field localization."
Sound quality includes characteristics of reproduction such as frequency range (bandwidth), accuracy of relative amplitude levels throughout the frequency range (timbre), range of sound amplitude level (dynamic range), accuracy of harmonic amplitude and phase (distortion level), and amplitude level and frequency of spurious sounds and artifacts not present in the original sound (noise). Although most aspects of sound quality are susceptible to measurement by instruments, in practical systems characteristics of the human hearing system (psychoacoustic effects) render inaudible or relatively unnoticeable certain measurable deviations from the "original" sounds.
Sound field localization is one measure of spatial fidelity. The preservation of the apparent direction, both azimuth and elevation, and distance of a sound source is sometimes known as angular and depth localization, respectively. In the case of certain orchestral and other recordings, such localization is intended to convey to the listener the actual physical placement of the musicians and their instruments. With respect to other recordings, particularly multitrack recordings produced in a studio, the angular directionality and depth may bear no relationship to any "real-life" arrangement of musicians and their instruments and the localization is merely a part of the overall artistic impression intended to be conveyed to the listener. In any case, one purpose of high-fidelity multi-channel reproduction systems is to reproduce spatial aspects of an on-going sound field, whether real or synthesized. As with respect to sound quality, in practical systems measurable changes in localization are, under certain conditions, inaudible or relatively unnoticeable because of characteristics of human hearing.
Even with respect to those recordings in which the localization is intended to convey the impression of being present at the original recording, the producer must choose among various philosophies of microphone placement and sound mixing and recording, each of which results in the capturing of sound fields that differ from one another. Apart from variations introduced by artistic and technical judgments and preferences, the capture of a sound field is at best an approximation of the original sound field because of the inherent technical and practical limitations in recording, transmission and reproducing equipment and techniques.
Numerous decisions, adjustments, and combinations available to a sound field producer will be obvious to one skilled in the art. It is sufficient to recognize that a producer may develop recorded or transmitted signals which, in conjunction with a reproduction system, will present to a human listener a sound field possessing specific characteristics in sound quality and sound field localization. The sound field presented to the listener may closely approximate the ideal sound field intended by the producer or it
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Davis Mark F.
Dolby Ray M.
Todd Craig C.
Dolby Laboratories Licensing Corporation
Gallagher Thomas A.
Knepper David D.
Lathrop David N.
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