An anthology of articles on Spatial Sound Techniques, Part 1: Virtual and Binaural Audio Technologies

Edited by Durand R. Begault

Copyright © 2004 Audio Engineering Society, Inc.Library of Congress Catalog Card No. 2004114099.ISBN No. 0-937803-53-7.First printing 2004 October (all rights reserved). Except for brief passages to be used in review or as citation of authority, no part of this book may be reproduced without prior permission from:Audio Engineering Society, Inc.60 East 42nd Street, Suite 2520 New York, New York 10165-2520, USA Telephone: +1 212 661 8528.Fax: +1 212 682 0477.

w m m m m im m m M m m m m ,

ContentsINTRODUCTION............................................................................Durand R. Begault 7

A. TECHNICAL OVERVIEW

Introduction..................................................................................................................................15

Introduction to Head-Related Transfer Functions (HRTFs): Representations of HRTFsin Time, Frequency, and Space. Corey I. Cheng and Gregory H. Wakefield(AES 107th Convention, New York [1999 September], Preprint 5026)..........................17

Digital Signal Processing Issues in the Context of Binaural and Transaural Stereophony. Jean-Marc Jot, Veronique Larcher, and Olivier Warusfel (AES 98th Convention, Paris [1995 February], Preprint 3980)............................................................46

B. HISTORICAL PAPERS AND EARLY RESEARCH INTO VIRTUAL AUDIO TECHNIQUES

Introduction................................................................................................................................. 95

Excerpts from “Binaural Transmission System at the Academy of Music in Philadelphia.” K. E. Hammer and W. B. Snow (Bell Telephone Laboratories, Internal Report 320311 -5 in Study o f Speech and Hearing at Bell Telephone Laboratories. The Fletcher Years, compiled by C. M. Rankovic and J. B. Allen (Reprinted with per­mission from the Acoustical Society of America [1932], Compact Disc)....................... 97

Binaural Sound Reproduction at Home. H. T. Sherman (JAES , vol. 1, pp. 142-145 [1953 January]).........................................................................................................................127

Binaural and Stereophonic Sound— In Retrospect. William H. Offenhauser, Jr. (JAES, vol. 6, pp. 67-69 [1958 April])................................................................................................131

Creating Source Elevation Illusions by Spectral Manipulation. P. Jeffrey Bloom (JAES, vol. 25, pp. 820-828 [1977 September])............................................................................ 134

Pinna Transformations and Sound Reproduction. C. A. Puddie Rodgers (JAES, vol.29, pp. 226-234 [1981 April])................................................................................................140Correction (JAES, vol. 29, p. 525 [1981 July/August]).................................................... 148

C. LOUDSPEAKER REPRODUCTION OF BINAURAL SOUND

Introduction............................................................................................................................... 151

Precision Sound-lmage-Localization Technique Using Multitrack Tape Masters. Toshinori Mori, Goro Fujiki, Nobuaki Takahashi, and Fumio Maruyama (JAES, vol. 27, pp. 32-38 [1979 January/February])................................................................................... 153

Controlling Sound-lmage Localization in Stereophonic Reproduction. Naraji Sakamoto, Toshiyuki Gotoh, Takuyo Kogure, and Masatoshi Shimbo (JAES, vol. 29, pp. 794-799 [1981 November]).................................................................................................................... 160

Controlling Sound-lmage Localization in Stereophonic Reproduction: Part II. Naraji Sakamoto, Toshiyuki Gotoh, Takuyo Kogure, Masatoshi Shimbo, and Almon H. Clegg (JAES, vol. 30, pp. 719-722 [1982 October])...................................................................166

Equalization and Spatial Equalization of Dummy-Head Recordings for Loudspeaker Reproduction. David Griesinger (JAES, vol. 37, pp. 20-29 [1989 January/February]) 170

Prospects for Transaural Recording. Duane H. Cooper and Jerald L. Bauck (JAES, vol. 37, pp. 3 -19 [1989 January/February])........................................................................180

Processing Artificial-Head Recordings. H. W. Gierlich and K. Genuit (JAES, vol. 37, pp. 34-39 [1989 January/February])...................................................................................197

The “Stereo Dipole”— A Virtual Source Imaging System Using Two Closely Spaced Loudspeakers. Ole Kirkeby, Philip A. Nelson, and Hareo Hamada (JAES, vol. 46, pp. 387-395 [1998 May])..............................................................................................................203

D. AURALIZATION AND SPATIAL REVERBERATION TECHNOLOGIES

Introduction...............................................................................................................................215

Image Model Reverberation from Recirculating Delays. Gary Kendall, William Martens, Daniel Freed, Derek Ludwig, and Richard Karstens (AES 81st Convention, Los Angeles [1986 November], Preprint 2408 )........................................................................ 217

Auralization—An Overview. Mendel Kleiner, Bengt-lnge Dalenback, and Peter Svensson (JAES, vol. 41, pp. 861-875 [1993 November])............................................235

Analysis and Synthesis of Room Reverberation Based on a Statistical Time-Frequency Model. Jean-Marc Jot, Laurent Cerveau, and Olivier Warusfel (AES 103rd Convention, New York [1997 September], Preprint 4629 )..................................250

E. PERCEPTION

Introduction...............................................................................................................................295

On Our Perception of Sound Direction. L. Rayleigh (Reprinted with permission from Philosophical Magazine, vol. 13, pp. 214-232 [1907])....................................................297

Some Particulars of Directional Hearing. K. de Boer and A. Th. van Urk (Reprinted withPermission from Philips Technical Review, vol. 6, pp. 359-364[1941 December])................................................................................................................... 306

Binaural Technique: Do We Need Individual Recordings? Henrik Moller, Michael Friis Sorensen, Clemen Boje Jensen, and Dorte Hammershoi (JAES, vol. 44, pp. 451-469 [1996 June])..............................................................................................................................312

Direct Comparison of the Impact of Head Tracking, Reverberation, and Individualized Head-Related Transfer Functions on the Spatial Perception of a Virtual Speech Source. Durand R. Begault, Elizabeth M. Wenzel, and Mark R. Anderson (JAES, vol. 49, pp. 904-916 [2001 October])......................................................................................... 331

F. HEAD-RELATED TRANSFER FUNCTION (HRTF) MEASUREMENT

Introduction............................................................................................................................... 347

Measuring a Dummy Head in Search of Pinna Cues. H. L. Han (JAES , vol. 42, pp. 15-37 [1994 January/February])..........................................................................................349

Repeatability Analysis of Head-Related Transfer Function Measurements.Klaus A. J. Riederer (AES 105th Convention, San Francisco [1998 September], Preprint 4846)...........................................................................................................................372

Head-Related Transfer Functions of Human Subjects. Henrik Moller, Michael Friis Sorensen, Dorte Hammershoi, and Clemen Boje Jensen (JAES, vol. 43, pp. 300-321 [1995 May])............................................................................................................................... 417

Objective and Subjective Evaluation of Head-Related Transfer Function Filter Design. Jyri Huopaniemi, Nick Zacharov, and Matti Karjalainen (JAES, vol. 47, pp. 218-239 [1999 April]).............................................................................................................................. 439

G. APPLICATIONS OF VIRTUAL AUDIO

Introduction............................................................................................................................... 463

Headphone System with Out-of-Head Localization Applying Dynamic HRTF (Head- Related Transfer Function). Kiyofumi Inanaga, Yuji Yamada, and Hiroshi Koizumi (AES 98th Convention, Paris [1995 February], Preprint 4011)...................................... 465

Virtual Acoustics, Aeronautics, and Communications. Durand R. Begault (JAES, vol. 46, pp. 520-530 [1998 June])............................................................................................... 490

Creating Interactive Virtual Acoustic Environments. Lauri Savioja, Jyri Huopaniemi, Tapio Lokki, and Riitta Vaananen (JAES, vol. 47, pp. 675-705 [1999 September]).501

Introduction...There is no “nonspatial hearing”

— J e n s B l a u e r t , S p a t ia l H e a r in g

F or years the process o f binaural fusion has been a mystery. Year a fter year new fa c ts have been slowly extracted— nature does not yield her secrets to the faint-of-heart.

— W il l i a m H. O f f e n h a u s e r , J r . , “Binaural and Stereophonic Sound— In Retrospect” JAES, V o l . 6 (1 9 5 8 A p r i l )

Audio engineers and their collaborators in the sciences and the arts have always had a keen interest in the po­tential for sound to com municate spatial perceptual

experiences. Fundamentally, we are very good at perceiving acoustical differences in the transformations of sound sources at the two ears, which allows the binaural hearing system to create acoustic imagery that is inherently spatial. Although we can choose to ignore the spatial aspects o f reproduced sound and focus on, for example, the semantic content o f the acoustical message, active attention to the richness and com­plexity of spatial attributes in audio reproduction makes for a satisfying, rich experience that continually fascinates audio­philes, engineers, and scientists and the “lay listener” as well.

Interest in spatial sound within the Audio Engineering So­ciety (AES) was at first prim arily concerned w ith stereo­phonic and quadraphonic sound reproduction. The AES an­thology Stereophonic Techniques (edited by John Eargle) can be considered the first collection o f AES papers con­cerned with spatial sound. The intention of the present an­thology is to historically pick up where this first anthology left off, and to represent the research concerned with the next generation of spatial sound techniques. I have attempted to give the reader a representative sampling of papers (primari­ly from the pages of the Journal o f the Audio Engineering Society and from AES convention preprints) that are con­cerned with binaural recording and the simulation of binaural recording using “virtual audio” or “3-D sound” techniques. This anthology does not include the topic o f multichannel surround sound, which is planned for a future volume as part 2 of the present anthology.

Assembled here is a collection of twenty-eight papers that serve both as basic references and as a story o f the evolution of binaural sound research into present-day 3-D sound tech­niques. Space (so to speak!) has naturally prevented us from including all o f the papers that might be considered, and their exclusion is by no means a measure of their quality. A search o f abstracts on the AES archive Electronic Library, which

lists papers through the year 2000, indicates no fewer than 172 docum ents for the term s “3-D sound,” “b inaural” or “HRTF, ’’m ost o f these occurring in a tw elve-year period starting in 1988. I identified representative topic areas for each chapter, and then selected a wide range of different au­thors who wrote in-depth papers on their topics. Excluded are papers from AES Proceedings, which should be consulted for additional relevant material in bound form (in particular, Spa­tial Sound Reproduction— Proceedings o f the AES 16th Inter­national Conference, Rovaniemi, Finland, 1999 April 10-12).

Two persons who have helped drive the A ES’ interest in binaural recording and 3-D sound processing deserve mention at the outset. First, there is Jens Blauert, the Richard C. Heyser distinguished lecturer at the AES 114th Convention and author of the landmark 1974 book Raumliches Horen and its English translation Spatial Hearing (1983, revised 1997). Jens Blauert introduced many people in the research community to a “com­munications engineering” approach to spatial hearing that em­phasized psychoacoustic research , signal processing, and acoustic engineering. Second, there is Manfred Schroeder, the Richard C. H eyser distinguished lecturer at the AES 111th Convention. Manfred Schroeder’s innovative contributions to spatial simulation techniques include reverberation simulation, binaural measurement, and crosstalk cancellation. He is the author o f m any AES papers, including the review paper, “Acoustics in the Audio Engineering Society” (AES Journal, Volume 46, pages 71-73, 1998 January/February). The work o f these two m en helped lay the groundwork of the support necessary for much of the research in the present volume.

HISTORICAL CONNECTION: STEREO AND FILM SOUNDSpatial sound in the context o f audio engineering is also tied historically to the development o f sound for cinematic pro­ductions. In 1911, Edw ard H. A m et described in his U.S. patent application, “M ethod and M eans for Localizing Sound Reproduction,” a technology for sw itching sound between

Spatial Sound Techniques: Part 1 7

m ultiple loudspeakers “ ...to reproduce different parts o f a sound record at different predetermined places, in such man­ner that the sounds accompanying an operatic, theatrical or other action may be appropriately located relative to their re­spective parts in the action” (U.S. patent 1,124,580 awarded in 1915). The introduction of Fantasound in 1938, the multi - ple-loudspeaker system used in the W alt Disney movie Fan­tasia, allowed for the movement o f sound images from loud­speaker to loudspeaker. It also encompassed the invention of the panoramic potentiometer, familiar today as the pan po t control on a mixer, which allows for the positioning of sounds not only at the location of a single loudspeaker but also at vir­tual image locations between loudspeakers.

Just a few years prior to this, engineers at Bell Laboratories in the United States and at EMI Laboratories in England had experimented with stereo recording and reproduction tech­niques for loudspeaker playback. Both laboratories were con­cerned with the encoding of multiple sound sources using a smaller number of recording and playback elements. Harvey Fletcher led the Bell Laboratories research team into early ex­periments in spatial sound reproduction technology. In one as­pect o f their research in the early 1930s, a hypothetical situa­tion was composed of an orchestra separated by a soundproof wall from an audience.1 The audience facing the soundproof wall is an analogy to persons listening to a broadcast of the music at a remote position. Hypothetically, a wall o f multiple microphones could be placed at all positions on the wall facing the orchestra; an equivalent number of loudspeakers on the other side of the wall would face the audience. This could (partially) reproduce successfully the acoustic wavefront and its associated spatial information; but clearly, it involved too many microphones and loudspeakers to be practical. They worked out that successful miking and playback of the multi­ple sources could be accomplished by a practical approach, which radically reduced the number o f recording and playback channels to only three. The acoustical w avefront was no longer reproduced, but the psychoacoustic criteria regarding the rep roduction o f sp a tia l ch a rac te ris tic s w ere ju d g e d adequate.

As early as 1881 there was a demonstration of the possibili­ties o f binaural transm ission at an exhibition at the Paris Grand Opera. Clement Ader designed a system using a series of eight microphones, mounted about a meter apart in front of an orchestral stage, which were connected to binaural tele­phone receivers at a remote location.2 W hile the system pro­duced spatial sound imagery for the listener, binaural record-

1 W. B. Snow (1953). “Basic Principles of Stereophonic Sound.” Journal o f the Society o f Motion Picture and Television E ngi­neers 61:567-589.2 Scientific Am erican (1981 Decem ber 3), reprinted in B. F. Hertz, “ 100 Years with Stereo: The Beginning.” Journal o f the Audio Engineering Society (1981) 29:368-370, 372; also in the AES anthology Stereophonic Techniques (J. Eargle, Ed.).

ing of multiple sources using a “dummy head” came out of la ter w ork at B ell L aboratories. A t the 1933 C entury o f Progress Exhibition, audience m em bers would listen over binaural headphones as demonstrators (more than one sound source) spoke in a soundproof room to “Oscar,” a modified tailor’s dummy with microphones in each cheekbone. Oscar is described in Chapter B of this anthology.

Alan Blumlein’s work in stereophony was the other early landmark in capturing and reproducing spatial sound.3 He re­alized early on that a reproduction o f the acoustic field by means o f two microphones and two loudspeakers was impos­sible. He discovered that creating a sound level difference be­tween two loudspeakers could successfully produce virtual im ages betw een the loudspeakers at various positions. In 1933 he patented a process o f capturing only the intensity dif­ferences of a wavefront using two-directional microphones, so that the relative angle of the sound sources to the micro­phones would produce virtual images along an arc between th e lo u d s p e a k e rs .4 T h is is k n o w n to d a y as in te n s ity stereophony, and is the most common method of encoding the spatial properties o f multiple sound source positions for two loudspeakers.

Numerous examples of binaural recordings came forth in the 1970s, particularly after the introduction by Sennheiser and N eum ann o f b inau ra l m icrophones fo r com m ercial recording. A revival o f sorts o f binaural techniques came about in the late 1980s, in connection with the first virtual en­vironment (“virtual reality”) systems. At the start o f the “in­ternet age,” many researchers and consumers were interested in synthesizing both visual and aural 3-D space. Not only was sound being processed binaurally to arbitrary positions, it was now connected to the same head tracking technologies that enabled the interactive nature of visual displays for virtual en­vironments.5 The improved capabilities o f audio signal pro­cessing that prompted the development o f 3-D audio systems referred to as “virtual sound” systems in the late 1980s be­came increasingly cheaper, and migrated to games and popu­lar entertainment. M ore recently, virtual surround sound sys­tems have becom e com mercially available, which simulate multichannel loudspeaker systems using headphones or two loudspeakers.

3 For additional historical perspective on Blumlein and Fletcher’s work, see S. P. Lipshitz, “Stereo Microphone Techniques: Are the Purists W rong?” Journal o f the Audio Engineering Society (1986) 34:716-744.4 A. D. B lum lein (1933). “Im provem ents in and R elating to Sound-Transmission, Sound-Recording and Sound-Reproducing Systems.” British Patent 394,325; reprinted in Journal o f the A u­dio Engineering Society (1958) 6:91-98, 130; also in R. Streicher and F. A. Everest (1998). The New Stereo Soundbook (2nd ed.). Pasadena: Audio Engineering Associates.5 E. M. Wenzel, F. L. Wightman, and S. H. Foster (1988). “A V irtual D isp lay System for C onveying T hree-D im ensional Acoustic Information.” Proceedings o f the Human Factors Soci­ety 32nd Annual Meeting, Anaheim, California.

8 Spatial Sound Techniques: Part 1

DEFINITIONS: BINAURAL SOUND, 3-D SOUND, AND EVERYTHING ELSE SURROUNDING YOUSpatial sound is a phrase often used interchangeably in ref­erence to several quite different concepts. G reater specifici­ty can clear up the potential for confusion. First, there are devices associated with recording and reproducing spatial sound, such as hardware and storage m edia (e.g., a dummy- head m icrophone or a DVD film w ith surround sound). Next, there is the spatial acoustic field, that is, the w ave­forms produced by the loudspeakers as m easured at the lis­tening position. This refers strictly to the physical phenom ­en a o f a c o u s tic a l w a v e fo rm s , as d is t in g u is h e d fro m hardware or perception. Finally, there is the perceptual sen­sation of spatial sound. A fundam ental exam ple endemic to recording engineering is localizing sounds at a specific lo­cation that does not correspond to the location o f the real sound source. For example, a stereo recording can produce spatial images at positions located between the loudspeak­ers, and some virtual audio processors can create im agery outside o f them . It is possib le for the sam e recording to cause a perceptual sensation o f being im m ersed in or sur­rounded by sound, as in a cinem atic audio production. In short, the spatial acoustic field can po ten tia lly resu lt in many different kinds of auditory spatial percepts for a giv­en listener.

In the endeavor to control the spatial acoustic field, an audio engineer functions more as a participant in the process o f cre­ation than as the final arbiter o f the spatial imagery heard by a listener. Like other qualitative perceptual features of sound re­production systems, spatial imagery is influenced by the non- linearity of the reproduction system and the acoustics o f the listening space. For example, a small room with reflective walls can modify spatial imagery, as can a large reverberant room. Using a spatial sound processor to produce a spatial acoustic field does not guarantee that a listener will hear it; on the other hand, one can have the sensation of being surrounded by sound even when listening to a monophonic loudspeaker. For many audio engineers the challenge is to produce a spatial acoustic field that will be perceived as satisfying for a wide va­r ie ty o f p la y b a c k h a rd w a re , se a tin g lo c a tio n s , and environments.

Binaural recording for purposes of this anthology refers to recordings made with a mannequin (“dummy”) head record­ing d ev ice (a lso re fe rred to by the G erm an e q u iv a le n t Kunstkopf). A dummy-head microphone consists o f a m an­nequin head with two microphones located at the position of the ears, and has been used since the 1930s to make record­ings that capture the spatial cues “heard” by the dummy head. There are com m ercially available systems for both “hi-fi”

6 B. B. Bauer. “ Stereophonic Earphones and B inaural Loud­speakers.” Journal o f the Audio E ngineering Society (1961) 9:148-151; reproduced in the AES anthology Stereophonic Tech­niques (J. Eargle, Ed.).

Spatial Sound Techniques: Part 1

recording and acoustic measurement, the former having mi­crophones located at the entrance of the ear canal, and the lat­ter including the ear canal transfer function. One can also pur­chase microphones that work on a stethoscope principle, with a real as opposed to a dummy head.

A characteristic o f binaural recordings is that they are very spatia lly conv incing over headphones, particu larly w hen headphone equalization is applied, but not so suc­cessful for stereo loudspeaker playback. Benjam in Bauer addressed this topic in the AES Journal as early as 1961.6 Eighteen years later the m atter was still being addressed, as seen in the papers included in C hapter C o f this anthology by David G riesinger and by Hans G ierlich and Klaus Genu- it. A nother characteristic o f binaural recordings is that once the spatial im agery is captured, it is difficult if not im possi­ble to reconfigure the spatial location o f the sound sources in postproduction. Interest in binaural recordings waxes and wanes in the audio industry. Its initial popularity was seen in the 1970s, after the introduction o f binaural m icrophones for com m ercial record ing by S ennheiser and N eum ann. There is current in terest in the surround sound recording com m unity for using dum m y heads as part o f the m icro­phone arsenal.

3-D sound (interchangeably referred to as “virtual audio”) refers to digital signal processing devices that emulate binaur­al sound, and that usually have added capabilities in terms of sound source location control, environmental simulation, and postrecording processing and equalization. The “binaural mixing consoles” first developed in the 1970s are the basis of most 3-D sound devices and software of today. The interest in virtual reality in conjunction with improved audio signal-pro­cessing capabilities made virtual audio increasingly popular from the 1980s onward, via inclusion in gaming products and due to dramatic cost reductions for digital signal processing.

Very simply, virtual audio works by processing each dis­crete input channel into two channels, using the interaural time and level differences and outer ear transforms that corre­spond to the spatial auditory cues for a specific direction (both azimuth and elevation). The concept is that the acousti­cal effect of a dummy head is accomplished “synthetically” via filters. Each single auditory source or track to be spatial- ized has its own filter pair that creates a two-channel left- and right-ear binaural signal at the output. For multiple sources the ind iv idual le ft-ear and rig h t-ea r b inaural signals are summed into a single output stream. The filter pairs contain the frequency, phase, and gain information corresponding to the binaural recording for a specific direction. This direction- specific filtering is obtained from measurements o f the head- related transfer func tion (HRTF) o f a dum m y head, a real head, or from modeled, averaged, or approximated HRTFs. C orey C heng and G regory W ak efie ld ’s “In troduction to Head-Related Transfer Functions (HRTFs): Representations o f HRTFs in Time, Frequency, and Space” in Chapter A of this anthology gives further explanation.

_ _ - —

The virtual imagery of 3-D sound is degraded compared to headphone listening when heard over a conventional stereo­phonic loudspeaker setup, due in part to the “crosstalk” of each loudspeaker across the head to the furthermost ear as well as to the nearest ear. With headphones an isolated path to each ear can be attained w ithout crosstalk , since the ears are acoustically isolated from one another. However, with loud­speakers a waveform is produced that is heard by both ears, which corrupts the intended spatial cues and therefore the quality or stability o f the virtual image. A solution known as “crosstalk cancellation” is described in several papers in Chap­ter C, “Loudspeaker Reproduction of Binaural Sound.” A re­cent book devoted to the topic was published by W illiam Gardner.7

A surround sound reproduction system is most obviously characterized by m ultichannel playback over several loud­speakers, in contradistinction to the two loudspeakers or head­phones associated with stereo or 3-D audio. There has recently been great emphasis in the professional and consumer audio markets worldwide on new surround sound products, research and technology, as demonstrated for instance by papers and exhibits at the Audio Engineering Society conventions. Virtual surround sound refers specifically to the virtual simulation of one or more surround sound loudspeakers using a 3-D sound system. The host environment of the loudspeakers may or may not be simulated as well (e.g., a dubbing stage). Typical de­signs for virtual surround sound systems that have been com­mercially available since around 1988 include:

• Actual loudspeakers located at the typical left, center, and right front positions for a surround sound system, with the rear and/or side surround channels produced virtually;

• Virtual creation of all surround sound channels from stereo headphones;

• Creation of surround channels and the center channel from ju s t tw o actual loudspeakers (see C ooper and B auck ’s “Transaural”8 technology, Chapter C).

Those working with 3-D sound techniques and crosstalk cancellation in the 1980s were very aware of the possibilities o f using two loudspeakers to supply surround sound, particu­larly for television. In particular there was great interest in the audio community in the mid-1980s in creating virtual sur­round sound because of the television industry’s recognition of the increasing viewing of films at home.

7 W. G. Gardner (1998). 3-D Audio Using Loudspeakers. Boston: Kluwer Academic.8 Transaural is a trademark of Cooper Bauck Corporation.9 R. Streicher and F. A. Everest. (1998). The New Stereo Sound- book (2nd ed.). Pasadena: Audio Engineering Associates.10 F. Rumsey (2001). Spatial Audio. Oxford: Focal Press.

10

By the mid-1980s, the concept o f the home entertainment center was in full swing, fostered by the development of large-screen television sets with stereo television sound, the widespread sales of video tape and videodisc players, and the rampant growth of neighborhood video rental shops. What had once been the sole province of the motion picture theater was now finding a familiar place in homes through­out society; movies shown on large screens and accompa­nied by m ultichannel sound system s w ere becom ing commonplace.9

V ery soon after the popularization o f stereo televisions and b roadcasts in the 1980s cam e spa tia l enhancem ent p rocesso rs fo r te lev ision sound and even the firs t “3-D sound” te lev ision broadcasts (e.g., sound effects for the “Tw ilight Zone” television show , produced at N orthw est­ern U niversity C om puter M usic in the m id-1980s). It oc­curred to m ore than one engineer that the sam e 3-D sound techniques used to form virtual im ages of arbitrary sound sources could be applied to creating surround sound from stereo te lev ision p layback, resu lting in several products and techno log ica l developm ents. A good rev iew o f the techniques involved in w hat is som etim es term ed “virtual hom e th e a te r” and o f sp a tia l sou n d in g en e ra l can be found in F rancis R um sey’s book Spatia l A u d io ,10

A uralization is a spatial sound technique that is distin­guished principally via its application. Auralization involves the combination of room modeling programs and 3-D sound- processing methods to simulate the reverberant characteris­tics o f a real or m odeled room acoustically. M endel Kleiner, B engt-Inge Dalenback, and Peter Svensson’s introductory paper is included in Chapter D. They state that “auralization is the process o f rendering audible, by physical or mathemat­ical modeling, the sound field of a source in a space, in such a way as to sim ulate the binaural listening experience at a g iv e n p o s it io n in a m o d e le d s p a c e .” A u ra liz a tio n so ftw are/hardw are packages use com puter-aided design (CAD) software and, in particular, sound system design soft­ware packages, and are concerned with realistic rendering of reverberation o f a given room. A coustical consultants and their clients are able to listen to the effect o f a modification to a room or sound system design and compare different so­lutions using virtual audio techniques. Com pared to tradi­tional methods using blueprints and scale models, an aural­iza tio n so ftw are /h a rd w a re sy stem allow s p h y sica l and perceptual parameters o f a room model to be calculated and then verified by listening, within the limits o f the accuracy of the reverberation modeling and 3-D sound presentation tech­niques used.

IN SUMMARY, THE FUTURE...I hope that the collection o f papers in both this and future an­thologies devoted to Spatial Sound Techniques will enthuse audio engineers and researchers by allowing easy access to

Spatial Sound Techniques: Part 1

interesting papers that otherwise would be distributed incon­veniently about the office or laboratory. M ore importantly, it may help to allow current and future researchers to lay the groundwork for improving audio reproduction in a manner that is more exciting in entertainment; more perceptually cali­brated and therefore more controllable, as addressed in Chap­ters E and F; and more useful in communications and human interface applications, as described in Chapter G. The choice of sound sources and the consideration of the listener’s asso­

ciations and experiences are also important factors in the de­sign of virtual acoustic displays. This is an area for future re­search that deserves greater attention and is outside the scope of the current anthology. These factors ultimately determine the level o f art involved in the application of virtual acoustics by the end user.

D u r a n d R . B e g a u l t , E d i to r N a s a a m e s R e s e a r c h C e n t e r

M o f f e t t F ie ld , CA 94035, USA

Durand R. Begault is recognized worldwide within the acoustic and psychoacoustic community as an important figure in the field of virtual acoustic 3-D audio systems and displays. He has been associated with the Human Information Processing Research Branch of NASA Ames Research Center, M offett Field, CA, since 1988. His research activities include development and evaluation of new audio and multimodal technologies for aeronautic and space applications. These technologies involve psy­chophysical evaluation of spatial hearing, speech intelligi­bility, and performance in virtual environment systems; room acoustic analysis and simulation; and improvement o f com m unications and w arning system s. H e is also active as an expert witness and acoustical consultant and serves as director of the Audio Forensic Center, Charles M. Salter Associates, San Francisco, CA.

Dr. B egault’s peer-review ed journal articles, patents, and books are cited in 57 U.S. patents and over 100 sc ien tific and eng ineering jo u rn a ls . H is 1994 book, 3-D Sound f o r V irtual R eality and M ultim edia, sold over 3000 copies. He is also the author o f an interac­tiv e C D -R O M on co m p u ter aud io p roduction p u b ­lished by A cadem ic Press and o f chapters in several acoustic and virtual environm ent reference books.

Dr. Begault is a member of the Acoustical Society of America, the Audio Engineering Society, and the Institute of Noise Control Engineering. His AES activities include: the organization of many workshops and paper sessions for AES conventions, chair o f the Technical Committee on P ercep tio n and S u b jec tiv e E v alu a tio n o f A udio Signals, and m em ber of the JAES Review Board since 1993.

Spatial Sound Techniques: Part 1 11