techtrends By Brian Dipert, Technical Editor

YOU MAY PLAN TO INCLUDE ONLY TWO SPEAKERS, JUST A SET OF HEAD- PHONES, OR SUPPORT FOR ONE- AND TWO-CHANNEL SOUND SOURCES IN YOUR NEXT DESIGN. NOT TO WORRY. PSYCHOACOUSTICS, PROCESSORS, AND PLENTY OF MEMORY CAN STILL GIVE YOUR CUSTOMERS AN IMMERSIVE AUDIO EXPERIENCE. “HEAR” IS HOW. Decoding and virtualization bring to the masses eople commonly use the terms “stereo,”“two channel,”and P“two speaker” to mean the same thing, but they’re committing an etymological error. “Stereo” derives from the Greek word stere- os, meaning “solid.” In other words, a stereo recording-and-listen- At a glance ...... 64 ing environment is one that reproduces the 3-D atmosphere of the Haven’t heard enough?...... 64 original performance. Bob Dylan’s Live speakers necessary to replicate the For more information...... 72 1966 ideally should sound just like it did acoustics of the listening environment. when first performed in Manchester, Monophonic , , and England, and Miles Davis’ Kind of Blue tape players, eventually supplanted by should transport you to 1959 and Co- their two-channel variants and by audio lumbia’s 30th Street Studio, New York, CDs, existed for reasons of the econom- even if you’re listening to them in your ics and technology limitations of the living room in Sacramento, CA, in 2001. time, not because they delivered realism. And, when the Tyrannosaurus Rex in the Some of you may be familiar with the ill- movie Jurassic Park growls on-screen, you fated quadraphonic (four-channel) sys- should hear it over your shoulder and 20 tems that briefly appeared in the early feet above you, and the hair on the nape 1970s. The theory behind quadraphonic of your neck should rise. audio was fairly solid, but the imple- As early as the 1930s, Bell Labs re- mentations weren’t. Manufacturers’ pro- searchers JC Steinberg and WB Snow de- prietary systems and corresponding me- termined that you need at least three dia were incompatible with each other, transducers to realistically reproduce an and compelling content was lacking. De- audio source (Figure 1a and b). Their re- luded audiophiles like to point to the fail- search didn’t comprehend additional ure of quadraphonic sound as justifica-

www.ednmag.com October 25, 2001 | edn 63 techtrends Surround sound tion for two-channel-only audio (Refer- other end of the line, within a group. AT A GLANCE ence 1). Another common argument of the au- The fact is surround sound in movie ୴ Armed with an auditory system under- diophile Luddites against audio with theaters has thrilled consumers for standing, a powerful-enough processor, more than two channels is the baffling decades. Leopold Stokowski and the and sufficient RAM and ROM, you can give statement that they need only two speak- Philadelphia Orchestra performed the your customers an immersive audio experi- ers because they have only two ears. In re- classical music in Disney’s (www.dis- ence no matter what the sound source is. ality, the human auditory system, work- ney.com) 1940 film Fantasia in Fanta- ing with other sensory faculties, such as sound, and it is but one early example ୴ Artificially created and artfully extracted vision, can accurately locate a sound of surround sound. Now-ubiquitous reflections and reverberations can both source in 3-D space using both absolute Dolby Surround first appeared in the approximate and alter the ambiance of the and differential time-of-arrival, intensi- mid-1970s, debuted with original recording environment. ty, and frequency cues along with train- the movie Batman Returns in June 1992, ing in how the head, shoulders, and ears and Jurassic Park followed in 1993 in ୴ Low- and high-frequency enhancement modify incoming sounds. Even if the DTS (Digital Theater Systems) sur- compensate for bass-deficient speakers and sound source is directly in front of you, round. Dolby Surround-encoded televi- lossy compression artifacts. the echoes and reverberations of the sion broadcasts and videotapes are now recording environment will alter it unless commonplace and, along with Dolby ୴ Interaural time and intensity adjust- the recording occurs in an anechoic Digital- and DTS-aware DVD and audio ments and head-related transfer-curve data chamber. Because the end listening en- CD players, have brought surround mu- enable you to place phantom sound vironment doesn’t have the same sic, movies, and other programs into liv- sources all around a listener. acoustics, you need audio processing to ing rooms and automobiles. DVD-Au- re-create a semblance of the original. dio and SACD (Super Audio Compact ୴ Speakers and headphones require dif- Now that listeners have enjoyed sur- Disc), assuming they succeed in the mar- ferent audio-processing schemes. round sound with portions of their tele- ket (which is not a foregone conclusion), vision programming, movies, and music will accelerate this awareness, as will im- collections, they’d like to extend immer- mersive gaming and other computer- tential surround-sound application, en- siveness to all of their multimedia expe- based audio environments (references 2 ables listeners to differentiate individual riences, regardless of the sources’ char- and 3). Teleconferencing, another po- speakers, talking at the same time at the acteristics—that is, monophonic or

HAVEN’T HEARD ENOUGH? If this article has whetted your ship is worthwhile if only for the papers on the Harman Web site plete sound field that occurs appetite to learn more about 10-issue-per-year Journal of the (www.harman.com). during an audio performance. surround sound, I encourage Audio Engineering Society. ● David Griesinger, principal ● Bob Stuart from Meridian you to check out references 1 to Most of the vendors listed in scientist at Lexicon, a division of Audio, the developer of the MLP 10 in the main article. Surround the “For more information...” Harman, provides a large num- compression scheme used in Sound Professional magazine sidebar have Web sites flush ber of his AES and other papers DVD-Audio and one of the key (www.surroundpro.com), which with white papers, application and presentations for free down- definers of the DVD-Audio stan- audio pioneer Tomlinson notes, other documentation, loading at www.world.std. dard, maintains the Acoustic Holman heads, is also an excel- presentations, and sound sam- com/~griesngr. You can even Renaissance for Audio Web site lent source of news and infor- ples. Each thinks its own see a picture of him sketching at www.meridian-audio.com/ara, mation and has particular appeal approach is the best, but, by Figure 3! which contains a number of to recording engineers. The surveying a number of them, ● Well-known interesting papers. magazine sponsors a conference you gain a breadth of knowl- Bobby Owsinksi runs Surround ● The Ambiophonics Web in Beverly Hills, CA, each edge on technology and prod- Associates, and the company’s site at www.ambiophonics.org December, as well as seminars uct alternatives. Web site at www.surroundassoci- discusses how to optimize the at the Consumer Electronics And speaking of Web sites, I ates.com contains several helpful acoustics of typical home listen- Show (www.cesweb.org) and list some that have been particu- articles. ing room environments. other forums. larly useful to me in my ● The FAQ is at ● The 3D Audio Immersion Speaking of conferences, the research. Fire up the Google www.stanford.edu/~mleese/Am site at www.3dai.net keeps up to biannual Audio Engineering (www.google.com) search bisonic/faq_latest.html. Also, date on the latest news in the Society (www.aes.org) conven- engine using keywords “sur- check out www.ambisonics.net world of surround sound. tion is an impressive group of round sound” to find hundreds for more information on this set Finally, watch for my Jan 10, some of the finest minds in of others. of techniques, developed in the 2002 cover story, which will audio, and the AES also spon- ● Floyd Toole, long-time and 1970s and intended for the describe and compare product sors periodic conferences on well-known audio researcher, recording, studio processing, alternatives, including complete audio topics. An AES member- has several detailed white and reproduction of the com- encoding/decoding systems.

64 edn | October 25, 2001 www.ednmag.com techtrends Surround sound two-channel—or the listeners’ settings, (spousal-acceptance factor)—many of strengths and the shortcomings of the such as in an automobile, an airplane, an them would like to gain an approxima- auditory system, along with some DSP office, a conference room, a living room, tion of the true surround-sound experi- horsepower and memory, can credibly or on the jogging track. But, because of ence using their current two-speaker or accomplish these seemingly divergent financial and aesthetic resistance to buy- headphone configurations. Fortunately, objectives (references 4 and 5). ing and installing center, rear, and sub- just as with lossy audio compression, an If you’re starting with a single-chan- woofer speakers—the so-called SAF in-depth understanding of both the nel—that is, monophonic—audio

STAGE SOURCE LOUDSPEAKER-BASE WIDTH B=2 TO 4m DIRECT-SOUND PULSE CENTER THREE MICROPHONES SCREEN 1 THREE ELECTRICAL CHANNELS LEFT RIGHT

THREE LOUDSPEAKERS SCREEN 2

Ϫ30Њ 30Њ THREE DISTINCT- SOUND PULSES

␤2 ␤1 AUDITORIUM OBSERVER THREE PULSES TO EACH EAR

(a)

STAGE Ϫ Њ SOURCE 100 100Њ DIRECT-SOUND PULSE SCREEN OF MICROPHONES ELECTRICAL CHANNELS VIRTUAL SOURCE Ϫ120Њ 120Њ SCREEN OF LOUDSPEAKERS LEFT RIGHT INDIVIDUAL POINT-SOURCE SPEAKER SPEAKER SOUND PULSES

SINGLE RESULTANT SOUND PULSE NOTES: O2 ␤ Њ AUDITORIUM 1. SCREEN 1'S LISTENING DISTANCE IS 3H (2 1=33 ), WHERE H IS HEIGHT. THIS DISTANCE IS POSSIBLY O1 MORE SUITABLE FOR A TV SCREEN. OBSERVERS 2. SCREEN 2'S LISTENING DISTANCE IS 2H (2␤2=48Њ), ONE PULSE TO EACH EAR WHERE H IS HEIGHT. THIS DISTANCE IS MORE SUITABLE FOR A PROJECTION SCREEN. (b) (c) H:SCREEN HEIGHT 3. SUBWOOFER IS NOT SHOWN; ITS LOCATION IS OPTIONAL.

CENTER

LEFT RIGHT 0Њ LEFT RIGHT HEIGHT Ϫ30Њ HEIGHT LEFT RIGHT 30Њ HEIGHT HEIGHT Ϫ45Њ LEFT 45Њ LEFT WIDE WIDE 45Њ 45Њ Ϫ Њ 0Њ 60 HIGH HIGH 60Њ Ϫ45Њ 45Њ 45Њ Ϫ90Њ 90Њ

SUBWOOFER SUBWOOFER 180Њ Ϫ90Њ 90Њ ON FLOOR ON FLOOR

Figure 1 LEFT SIDE RIGHT SIDE Ϫ120Њ 120Њ RIGHT-SIDE- DIFFERENCE DIPOLE

LEFT-SIDE- Њ DIFFERENCE DIPOLE 180 (d)

CB

Bell Labs research in the 1930s suggested that you need at least three speakers (a, courtesy Focal Press) to credibly reproduce a sound source (b, cour- tesy Focal Press). The 5.1-speaker configuration is common in today’s home-theater settings (c, courtesy Focal Press), whereas Tomlinson Holman’s 10.2-speaker proposal suggests one possible future arrangement (d, courtesy Tomlinson Holman Labs).

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source, it might seem impossible at first APPROXIMATELY A 100-Hz + glance to create a two-channel variant— HIGHPASS FILTER + never mind a full-blown sur- + Figure 2 LEFT OUTPUT round-sound representation—of + it (Reference 6). Recall, though, that peo- APPROXIMATELY ple generally regard low-frequency 2- TO 10-mSEC B + sounds as nondirectional; that is, the hu- MONOPHONIC DELAY INPUT + man auditory system can perceive them Ϫ + RIGHT OUTPUT no matter what location in the listening APPROXIMATELY area they come from. Therefore, you can 100-Hz LOWPASS FILTER apply a lowpass filter to the source and direct frequencies of less than 100 Hz or so only to those channels whose trans- ducers will likely be able to reproduce the Frequency subdivision, followed by time delay and mixing, is one means of converting monophonic frequencies, such as a distinct 0.1 sub- audio into a two-channel representation that retains monophonic-speaker backward compatibility woofer channel. (courtesy DV Magazine). Next, delay the highpass-filter output by an adjustable amount of time if you seat rows or in which the listeners are one of the two channels; the “stereo- want to allow for user customization and milling about instead of remaining in wide”button in low-end consumer-elec- then add it to the nondelayed signal to one location, requires a wide, deep sweet tronics gear frequently activates this nor- create one output channel and subtract spot. A similar situation exists in auto- mally undesirable technique. This tech- it from the nondelayed signal to create a mobiles, in which neither the driver nor nique obliterates center imaging of second channel (Figure 2). The results any of the passengers is in an ideal lis- shared-channel content. A more elabo- are true and complementary comb fil- tening location. Bigger sweet spots result rate technique that less destructively scat- ters, and, when you present the two chan- in a more immersive surround-sound ters the sound-source-directional cues nels through two speakers, the frequen- experience at the possible expense of re- involves first calculating the channel cies split evenly between them. Running duced sound-source-positioning preci- (AȕB) and (BȕA) information and then both channels through the same speaker sion. employing frequency-dependent time, cancels out the delay and re-creates the The sweet-spot characteristics also de- spectrum, and overall intensity alteration original monophonic signal. Advanced pend on the anticipated placement of the to create the perception that the sound technologies from some of the compa- two front speakers and on the geometri- is originating beyond the physical nies that the sidebar “For more infor- cal relationship between their spacing boundary of each speaker. mation...” lists employ more elaborate and the listener’s location. If the speakers Next, how do you create listening- filtering techniques to transform mono- are several yards apart, as with most au- room acoustic effects for the rear sur- phonic audio. Patent searches and con- dio/video receiver setups, the sweet spot round speakers? First, you must differen- ference papers reveal some clues on these is naturally wider; however, the center- tiate among early reflections, echo, and advanced techniques, but you must sign perceived location of audio material that late reverberations (Figure 3). These a nondisclosure agreement to get all the they share is indistinct. Adjacent trans- three phenomena result from sound re- details (see sidebar “Haven’t heard ducer placement, such as with speakers flecting off objects before entering listen- enough?”). In contrast, some simple and on either side of a television tube or com- ers’ ears, but the auditory system per- cheap pseudo-two-channel algorithms puter display, creates a narrow sweet spot ceives them in different ways. Early simply subdivide the audio into multi- but a well-defined center location for di- reflections—those lagging behind the frequency bins, allocating the bins alogue and other common material. To original sound by as much as 30 msec— among the various channels. enhance the center-channel characteris- enable the ear and brain both to locate the Now, you’ve got a two-channel audio tics, you determine what material the sound source and to perceive the room clip, either as an original recording, front left and right channels share and dimensions. Their amplitude depends on which, let’s assume, contains no matrix- then emphasize it using HRTF (head-re- the reflectivity of objects the sound waves encoded center and mono-surround in- lated-transfer-function) transforma- bounce off before entering your ear, formation, or one resulting from the ear- tions. Ideally, center-channel informa- whereas their delay is a function of room lier mono-to-two-channel conversion. tion transmits through a dedicated width, depth, and height and of the pres- Next, you might want to first alter the speaker, because a “phantom center,” ence of reflective objects within a room. “sweet spot,” or region within which a which you create by coupling the left and We perceive direct reflections—those person listening to the audio can hear right front speakers, exhibits timbre that that bounce off only one or only a few both channels. For a computer user sit- differs from the real thing. objects before entering the ear—as ting before a display, the sweet spot can In addition to emphasizing the shared echoes beyond 30 msec; hence, these re- be narrow and shallow, which often re- information, you might also want to flections tend to degrade the sound. Con- sults in more accurately perceived sound broaden the audio image created by data versely, sounds that have been reflected positioning and which is particularly ap- in one channel and not in the other. One many times with attenuation at each re- pealing with 3-D games.A home-theater quick and dirty means of accomplishing flection point come at a listener from all setting, in which listeners may be in 10- this goal involves inverting the phase of directions. Many of these low-amplitude,

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DIRECT diffuse late reflections, or reverberations, SOUND simultaneously arrive at the listener. A EARLY certain amount of reverberation is gen- SOURCE REFLECTION EARLY erally desirable. Think, for example, how REFLECTIONS LATE much richer your voice sounds when you REVERBERATIONS LEVEL sing in the shower. Conversely, in rooms DIRECT LISTENER with little reverberation, the sound you hear is often unpleasant. You create the perception of re- EARLY Figure 3 REFLECTION flections and reverberations by TIME employing RAM-based delay lines, along with signal processing, to modify the au- The auditory system perceives early reflections, echo, and late reverberations in different ways dio as a real-life reflection would. Differ- (courtesy Focal Press). ent delays, intensities, and spectral trans- formations can create the illusion of a operations. Mix and play back 100- and to create the illusion of more speakers cavernous concert hall or an intimate jazz 150-Hz tones in an audio-editing pro- than actually exist. Recall that, in the ITU club.Artificial ambiance seems appealing gram, and you’ll also hear what sounds configuration, each ear of each listener in theory, but reality is often under- like a 50-Hz tone. At the high end of the perceives sounds that originate from all whelming, especially if a listener exag- frequency spectrum, Kenwood’s (www. six speakers. Interaural time differences gerates the effect. An acoustical model kenwood.com) Supreme technology in- play a key role in locating sound sources that sounds good with a symphony or- terpolates high-order fundamental tones of frequencies of 1 kHz and lower (Fig- chestra, for example, might sound horri- from lower-order harmonics that have ure 4). Conversely, interaural intensity ble with a solo pianist or vocalist. Short survived lossy encoding. Thomson Mul- differences are the primary means by cuts in memory and processing power to timedia’s (www.thomsonmultimedia. which the auditory system locates the reduce system cost and power consump- com) MP3pro compression scheme takes source of sounds higher than 1 kHz. tion leave the resulting reverberation similar advantage of harmonics to shift When a sound source is close to a listen- sounding artificial. Artificial ambiance high frequencies beneath harm’s way er, the spherical outward radiation of also clashes with other ambiance already during encoding, subsequently restoring sound emanating from an off-center in the audio. them during decoding. source and the resulting level difference An alternative approach is more pro- At this point, you’ve created front left between the ears of the listener are addi- cessing-intensive but more authentic in and right channels, a center channel, one tional factors in determining location. its results. It involves analyzing and ex- or more rear channels, and maybe even The unique shape of each person’s head tracting this existing ambiance and send- a subwoofer channel. Today’s most com- and shoulders is an appreciable barrier to ing the reflections and reverberations to mon ideal reproduction setting is a six- and spectral modifier of sound waves, the rear channels. Audio engineers cap- speaker setup like the one that the and the spacing between ears, shape of ture this ambiance during the original ITU (International Telecommunication each ear, and shape of the auditory canal recording by using binaural, hypercar- Union) defines (Figure 1c). Aesthetic leading to the eardrum are also key iden- dioid, or omnidirectional microphones, considerations can drive subwoofer tifiers of a sound’s direction. or they can add the ambiance to the au- placement because the channel’s sound HRTF curves summarize these listen- dio during mixing—a high-tech version isn’t directional. However, if you place er-specific phenomena. By transforming of singing in the shower. Directing re- the subwoofer against a wall, especially in a sound’s timing and frequency spectrum flections and reverberations to the rear the corner of a room, you will perceive its using the HRTF data, you can theoreti- speakers can be an effective arrangement sound as the loudest. For music repro- cally “place” a sound anywhere in space in an automobile. The traditional auto duction, all other speakers should have around a listener’s head using only two audio configuration replicates the right full frequency response, and the sur- speakers. Some algorithm developers and left audio channels in both the front round-sound speakers should be direct- claim that an audio engineer can employ and the rear speakers. This so-called ly radiating. Conversely, for movies, the basic amplitude-based rather than the dual-stereo configuration significantly center channel often carries only dia- more elaborate HRTF-based alternatives diminishes the listeners’ appreciation: logue, and the surround-sound speakers to give the illusion of a sound moving The speakers not only are in poor loca- find most use in reproducing special ef- from front to back. Some algorithm de- tions but also bombard your ears with fects. Such home theaters often employ velopers claim that if an audio engineer destructive crosstalk from both the front bipole or dipole surround-sound speak- has employed basic amplitude-based ef- and the rear. ers for immersiveness. Unfortunately, fects rather than more elaborate HRTF- After creating additional audio chan- they also often trade off speaker fre- based techniques to give the illusion of a nels, you might also want to enhance the quency response and other characteris- sound moving from front to back, an perceived low frequencies of the audio to tics to reduce cost. HRTF-aware virtual-surround-sound compensate for anticipated bass-defi- system can deliver a more realistic result cient speakers or the high frequencies to TWO-CHANNEL VIRTUALIZATION than a front- and back-speaker combi- counterbalance the effects of lossy com- What if having more than two speak- nation. Because our ears are on the sides pression. Harmonics play a part in both ers isn’t an option? In this case, you need of our heads, we’re particularly sensitive

70 edn | October 25, 2001 www.ednmag.com techtrends Surround sound to shortcomings in “phantom”midlater- with headphones, in which each channel al speakers, which HRTF trans- FRONT is isolated to only a single ear. Uncom- forms account for, particularly if Figure 4 CENTER pensated audio, intended for speakers those transforms also adjust for interau- SOURCE but played back through headphones, ral crosstalk effects. ␪ PATHS TO produces an annoying in-the-head effect, LISTENER'S Conversely, when a front-placed TWO EARS compared with a compensated alterna- speaker pair creates virtual surround, it’s rsin␪ tive, which mixes each channel with a difficult to spin a psychoacoustically al- r␪ time-delayed and spectral-modified ver- tered sound completely around to the ␪ sion of the opposite. back of your head and equally challeng- r HRTF transformations for virtualiza- ing to communicate sound source height LEFT RIGHT tion with more than two speakers over cues. If you’re playing a video game, your EAR EAR headphones take a different form from head is stable and centered, and you also their two-speaker equivalents. Because FALSE have visual “suggestions” in the form of SOURCE the speakers are on the ears and follow on-screen objects to aid in locating the head regardless of its orientation, sound. However, in the absence of visu- sweet-spot issues disappear, more real- Њ al assistance, you may experience front- REAR CENTER istically achieving full 360 sound place- versus-back location confusion. In real ment and convincing vertical position- life, you’d turn your head to help find the Frequency-dependent interaural time and inten- ing. However, the direct coupling of the sound. But, because the sound’s location sity differences enable the ears and brain to transducer to the ear effectively removes is virtual and the HRTF-transformation determine a sound source’s location, but lack- outer-ear HRTF effects, which can make effect depends on your head’s orientation ing collaborating visual or head reorientation it difficult to achieve consistent results to the real speakers, this reflex reaction cues, these differences may result in front-ver- from user to user. Headphone-virtual- makes the problem worse. sus-back confusion (courtesy Focal Press). ization algorithms are also sometimes Ideally, HRTFs should be customiz- complicated because they can’t use the able for each listener, because we all have by, it does not serve as a point source.) acoustics in the listening room to help different head shapes, ear spacings and When audio engineers mix music and recreate the original environment. On contours, and concha openness and movie soundtracks, they assume that the other hand, if the listening-room depth. Multilistener environments ob- users will play the end results on tradi- acoustics are detrimental (echo-con- viate the effectiveness of such cus- tionally placed speakers. As noted, even ducive, for example), you should proba- tomization, however. Some HRTF algo- in a simple two-speaker configuration, bly begin with a “clean slate.” rithms also adapt their responses to each ear senses not only the output of its To achieve more realistic reproduction plane sound sources, to nearby sources corresponding front speaker, but also a of sound-source height (think of a rock- where spherical effects are important, spectrally modified and time-delayed et taking off) and to improve the real- and to listeners who are not in the sweet version of the opposite speaker. Howev- ism of front-to-back and back-side-to- spot. (For example, when a train speeds er, this acoustic crosstalk doesn’t occur side sound source movement, audio

FOR MORE INFORMATION... For more information on products such as those discussed in this article, go to www.ednmag.com and click on the Reader Service link under the Tools & Services section. When you contact any of the following manufacturers directly, please let them know you read about their products in EDN. Ambiophonics Fosgate Audionics Lucasfilm THX Spatializer Audio 3D Audio Immersion www.ambiophonics.org www.fosgateaudionics.com www.thx.com Laboratories www.3dai.net Enter No. 341 Enter No. 347 Enter No. 353 www.spatializer.com Enter No. 364 Enter No. 359 Bell Labs 4Front Technologies Meridian Audio WaveArts www.bell-labs.com www.oss3d.com www.meridian-audio.com SRS Labs www.wavearts.com Enter No. 342 Enter No. 348 Enter No. 354 www.srslabs.com Enter No. 365 Enter No. 360 Creative Labs Harman International QSound Labs www.creative.com www.harman.com www.qsound.com Surround Associates Enter No. 343 Enter No. 349 Enter No. 355 www.surroundassociates.com Enter No. 361 DFX Power Technology Kenwood Sensaura www.fxsound.com www.kenwoodusa.com www.sensaura.com Thomson Multimedia SUPER INFO NUMBER Enter No. 344 Enter No. 350 Enter No. 356 www.thomson- For more information on multimedia.com the products available Digital Theater Systems Lake Technology Enter No. 362 from all of the vendors www.dtsonline.com www.laketechnology.com www.sony.com listed in this box, go to Enter No. 345 Enter No. 351 Enter No. 357 Tomlinson Holman Labs www.ednmag.com, click www.tmhlabs.com on the Reader Service Dolby Labs Lexicon Sorient Enter No. 363 link, and enter no. 366 www.dolby.com www.lexicon.com www.softamp.com Enter No. 346 Enter No. 352 Enter No. 358

72 edn | October 25, 2001 www.ednmag.com techtrends Surround sound

pioneer Tomlinson Holman advocates a References ISBN 0-240-51623-0, Focal Press, 10.2-channel system (Figure 1d). His ap- 1. Guttenberg, Steve, and Brent But- Woburn, MA, 2001. proach builds on the 5.1-channel ITU terworth, “Stereo vs 5.1: Is more 10. Coulter, Doug, Digital Audio Pro- standard with the addition of dual side— more....or less?,”Stereophile,August 2001, cessing, ISBN 0-879-30-566-5, CMP that is, midlateral—channels, a rear cen- pg 49. Media, Lawrence, KS, 2000. ter channel, dual subwoofers, and two 2. Dipert, Brian, “‘Bassless’ buzz im- height channels. The height channels pairs advanced audio’s image,”EDN,May Acknowledgments target reproduction over speakers Ϯ45Њ 24, 2001, pg 20. Thanks to Andrew Reilly from Lake Tech- horizontally and 45Њ vertically away from 3. Dipert, Brian, “Security scheme nology, Scott Willing from QSound Labs, the listener. As an interim step to 10.2 doesn’t hold water(marking),”EDN,Dec Randy Roscoe from Spatializer Audio Lab- channels, several 6.1-channel approach- 21, 2000, pg 35. oratories, and Alan Kraemer from SRS es are gaining popularity. Dolby Digital 4. Dipert, Brian,“Digital audio gets an Labs, for their assistance and feedback. Surround EX, which Dolby Labs devel- audition: part two, lossy compression,” oped with Holman, matrix-encodes a EDN, Jan 18, 2001, pg 87. Author’s biography rear center channel, as does DTS-ES Ma- 5. Dipert, Brian,“Digital audio breaks Technical Editor Brian trix. DTS-ES Discrete employs a distinct the sound barrier,”EDN, July 20, 2000, pg Dipert experiences sur- rear center channel; Digital Theater Sys- 71. round sound every tems designed its bit-stream format to be 6. Rose, Jay, “Stereotypes,” DV Maga- time the four dogs lying backward-compatible with respect to ad- zine, September 2001, pg 98. around him in his ditional audio channels; higher precision 7. Layton, Leonard, “Surround sound office sense that the sample sizes; and higher sampling fre- takes to the air,” IEEE Spectrum, August mailman’s at the front door. You can reach quencies, such as the upcoming 24-bit, 2001, pg 56. Brian at 1-916-454-5242, fax 1-916-454- 96-kHz DTS. And THX Ultra2 technol- 8. Kraemer, Alan, “Two speakers are 5101, [email protected], and see his ogy extracts seven full-range channels better than 5.1,” IEEE Spectrum,May four-legged children’s pictures at www. and a subwoofer channel from 5.1-chan- 2001. bdipert.com. nel source material.˿ 9. Rumsey, Francis, Spatial Audio,

74 edn | October 25, 2001 www.ednmag.com EARS-ON ANALYSIS After reading this article, you audio/video receiver, supporting capabilities. My Labtec (www. enhancement in hardware. may get a sense that I’m a sur- Dolby Digital and DTS decoding, labtec.com) LCS-2414 speakers In my car, I have a 4.1-chan- round-sound enthusiast. Well, and connected to a Toshiba include a “3-D-stereo” adjust- nel speaker system. I have no you’re right. I’m surrounded by (www.toshiba.com) SD-2108 ment knob, and I’ve installed a desire to cut into the dashboard; surround sound in my home, DVD player (with Spatializer variety of audio-enhancement therefore, I have no center office, and car. Labs’ (www.spatializer.com) N-2- plug-ins for MusicMatch Juke- speaker. I also have a Sherwood My living room unfortunately 2 virtualization) and Mitsubishi box, Real Player, Real Jukebox, (www.sherwoodusa.com) XCM- and typically has less-than-ideal (www.mitsubishi-tv.com) SR- WinAmp, and the Windows 7370 AM/FM and CD play- acoustics. It does have a 5.1- HD5 HDTV receiver via Belkin Media Player. Many of the PCs’ er, X-DTS80 audio decoder, and channel speaker setup, compris- (www.belkin.com) coaxial and DVD software packages support an AX-6275 multichannel ampli- ing Dahlquist front speakers, a optical cabling. Dolby Headphone, all can virtu- fier. The X-DTS80 decodes DTS KLH (www.klhaudio.com) center The four desktop PCs in my alize Dolby Digital and Dolby audio CDs, and it also supports and direct radiating rear sur- house contain Analog Devices’ Stereo, and InterVideo’s (www. SRS Labs’ CircleSurround algo- round set, and an AudioSource (www.analog.com), now-defunct intervideo.com) WinDVD 3.0 rithm for one- and two-channel (www.audiosource.net) SW Aureal, Creative Labs (www. even decodes DTS. QSound’s audio sources. It almost makes Fifteen subwoofer. Driving the creative.com), and Zoltrix (www. (www.qsound.com) UltraQ and me wish I had a long commute speakers is a Technics (www. zoltrix.com) audio subsystems, SRS Labs’ (www.srslabs.com) to work. panasonic.com) SA-DX1050 each providing virtual-surround WOW Thing deliver audio