Unless you've been asleep under a rock for the past ten years, you've at least heard about surround sound. During the past several years, it has had a serious impact on movie soundtracks, and it could replace stereo as the de facto music-listening standard. But surround is a new format, and lots of myths, misinformation, and misconceptions about it are floating around. So if you're not sure what terms like AC-3, DTS, DVD-A, and 5.1 mean, you're in good company.
You can provide customers with a multichannel surround-sound experience in two different ways. In one method, a number of audio processors synthesize a multichannel signal from 2-channel stereo sources, but no magic surround processor will transform an existing stereo mix into a proper surround mix. Most home-theater systems have some sort of "ambience" setting for this purpose, but it's the worst-sounding effect you can imagine. A few of the more advanced processors include "matrix" modes, some of which work pretty well, but these modes will never equal a true 5.1-surround mix.
A much better option is to create original multichannel mixes from scratch. Mixing in 5.1 surround requires some extra equipment, which means learning some new techniques. But it's worth the effort; mixing music in 5.1 surround is the most exciting thing I've been involved in. We are witnessing a milestone in audio history. Millions of home-theater systems in the United States can play back surround music mixes and movie soundtracks. It's time for the recording industry to put out surround product - and it's not as difficult as you might think.
Early Birds And Worms
I'll start with a little historical perspective. You're probably familiar with monaural (aka mono) sound: you deal with only one channel of music information. The information can be as simple as a cheap clock radio with a tiny 1-inch plastic speaker or as complex as a concert sound system with dozens of triamped cabinets in large speaker stacks.
Of course, stereo is our standard listening format today. In stereo, you work with two distinct information channels, and you can position various instruments between two speakers typically arranged in front of the listener in an approximately 60-degree spread. This technique allows for some pretty cool psychoacoustic tricks which make the sound seem to emanate from a position between the speakers, even though no sound source exists in the center. This is called virtual, or phantom, center.
You can produce a stereo sound field, or soundstage, in a variety of ways. The easiest is to use a pair of microphones on a live group and direct these two channels to the speakers. But most music today is recorded in multitrack format. The channels are panned left, right, or in between at mixdown, creating an artificial soundstage.
Of course, stereo has been king for more than 30 years. The industry made a brief excursion into quadraphonic (4-channel) sound back in the 1970s, but squeezing four channels of music into a single record groove was beyond the technology's capabilities. A small group of home experimenters actually set up quad systems, and a few music recordings were released on LP and 4-track reel-to-reel tape. However, quad died an ignoble death, and many people ended up with expensive gear and nothing notable to play on it. The industry never really recovered from this brief affair with quad. To this day, you can make many record executives jump by mentioning the "Q word."
The movie industry revived the idea of surround sound. Aside from the incredibly ingenious multichannel soundtrack of Disney's Fantasia, the first real breakthrough was Dolby Surround, which offered left, center, and right front channels as well as a monaural, limited-bandwidth rear channel for special effects, such as the sound of Superman flying overhead. This mono rear channel was normally reproduced with two speakers to the sides of the listening area.
However, squeezing four channels of sound information onto the two audio channels of 35 mm film proved an imperfect solution. Playback with different Dolby Surround decoders could vary radically. More advanced decoders, such as Dolby Pro Logic, were designed, but they all suffered from the dreaded "phase-steering" problems, in which a level change in one channel could affect the mix in the other speakers.
Enter the digital age. The development of the compact disc in the early 1980s provided a way to deliver large amounts of digital data. Bits is bits, so the same bits could represent a graphic picture, your accounting information, or more audio. Tomlinson Holman (the "TH" in THX) was one of the leaders in surround sound in those days, and from his experiments with movie soundtracks, the term 5.1 (pronounced "five point one") was born.
The 5.1 format defines six discrete channels: five full-bandwidth channels (20 Hz to 20 kHz), and one low frequency effects (LFE) channel (the "point one" in 5.1) with a frequency response rated from 5 to 125 Hz. The LFE channel requires a specialized speaker, called a subwoofer, which reproduces only low frequencies. Few, if any, subwoofers can reproduce 5 Hz; most can reach down to 30 or 35 Hz before they roll off, and a few of the more expensive ones can go to 20 Hz. The channels are designated left, right, center, left surround, right surround, and LFE.
The bright people at Dolby Laboratories figured out how to digitally compress these six channels of information into a form that would take up less bandwidth than two stereo PCM tracks, and the Dolby Digital codec (coder-decoder) was born. Also known as Dolby AC-3, this codec is used on many current DVD movie soundtracks, and it is part of the High-Definition Television (HDTV) standard.
The situation remained static for a few years, but with the release of the movie Jurassic Park, a competing codec was introduced by Digital Theater Systems (DTS). The DTS codec (DTS is the name of both the format and the developer) uses less data compression and requires more bandwidth and data-storage space than Dolby Digital, so some DTS movies don't quite fit on a single DVD. However, the tracks have the potential to sound more like the discrete PCM tracks from which they were derived than is possible with Dolby Digital.
DTS pioneered a way to use the same format on a Red Book CD, but with compressed DTS data in place of PCM stereo audio. DTS also formed a record label to produce remixed 5.1-surround versions of stereo releases. Many of these remixes were done by the engineers who handled the original mixes. Currently, you can buy more than a hundred 5.1 DTS titles, including work from such artists as Steely Dan, Lyle Lovett, and the Eagles.
To play these CDs, you need a CD or DVD player with a digital audio output that can send the DTS bitstream to a DTS decoder, which extracts the six channels of information and converts them to analog. (Early DVD players have a digital output, but they don't recognize the DTS bitstream. Most consumer CD players don't have a digital output, and those that do might not recognize the DTS bitstream.) You also need six channels of amplification and speakers.
Back To Basics
I'll start at the beginning of the mixing chain and go through it step-by-step. You need some special items to mix in 5.1 surround, but most studios already possess 90 percent of the needed equipment. Once you add a few select pieces, you could be mixing surround music in your own studio.
The first thing you need is a multitrack master of the tune you want to mix. The multitrack format is not an issue; it can be as simple as an 8-track analog tape deck or as complex as a pair of 48-track digital decks. I've done some really cool 5.1-surround mixes using 16- and 24-track ADAT systems. The source tracks can be in any digital or analog format, including a computer workstation. Of course, you want tracks with excellent production values.
You need to route the recorded tracks into a mixing console that lets you pan them between five output channels. (There should also be a sixth output for the LFE channel, but you don't pan anything from the main tracks to this output.) If you have a Yamaha O2R or O1V, Panasonic DA7, Tascam TDM4000, or Mackie Digital 8-Bus, you're already in business. Each of these digital consoles lets you patch the outputs from the surround matrix (outputs) to an 8-channel mixing deck (more on this shortly).
If you don't have a console with built-in surround panning, it's relatively simple to patch the equivalent using sub-groups or aux sends. But for ease of mixing, nothing beats a screen with a picture of the room and a cursor that shows where the sound ends up. Some consoles, such as the DA-7, provide a pair of controls on the work surface to pan left/right and front/rear, while others, such as the Mackie D8B, use a trackball or mouse.
Patch the console's outputs to an 8-track deck, where your final surround tracks will reside. The Tascam DA-88 has become the standard multitrack deck for surround due to its popularity in the film industry, but any common 8-track format will work, including a computer workstation. You don't need a Dolby Digital or DTS encoder to mix surround tracks; encoding is the last part of the process. Whatever you record your mix on, carefully note the track assignments. Unlike stereo, surround gives you many different track-assignment methods to choose from.
Often you won't be able to choose which channels end up on what tracks. For instance, both the Panasonic DA7 and the Mackie D8B mixers are set up in mode 4, whereas many large-format consoles and some mixing programs (such as Minnetonka's MX 51 for Windows) are designed to be used in Mode 1. Try to pick one output format and note it on the label of every 5.1 tape you make. Eventually, someone will have to figure out your track assignments to encode them on a disc, and you don't want your sloppy work habits to jeopardize a project. This is an excerpt from the following article: You're Surrounded.
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