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 surround sound 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 radios, phonographs, 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 e 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 e 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, Dolby Digital 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 e 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 e 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 e 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. c David Griesinger, principal c 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, c Well-known audio engineer interesting papers. magazine sponsors a conference you gain a breadth of knowl- Bobby Owsinksi runs Surround c 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 c The Ambisonics FAQ is at c 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- c 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 2307 307 THREE DISTINCT- SOUND PULSES b2 b1 AUDITORIUM OBSERVER THREE PULSES TO EACH EAR (a) STAGE 2 7 SOURCE 100 1007 DIRECT-SOUND PULSE SCREEN OF MICROPHONES ELECTRICAL CHANNELS VIRTUAL SOURCE 21207 1207 SCREEN OF LOUDSPEAKERS LEFT RIGHT INDIVIDUAL POINT-SOURCE SPEAKER SPEAKER SOUND PULSES SINGLE RESULTANT SOUND PULSE NOTES: O2 b 8 AUDITORIUM 1. SCREEN 1'S LISTENING DISTANCE IS 3H (2 1=33 ), WHERE H IS HEIGHT.