(Click image for larger view) FIG. 1: You’ll need two multitrack decks: one for the source tracks and an 8-track deck for five full-bandwidth tracks, an LFE track, and a separate stereo mix. The receiver includes bass management, which redirects low-frequency information in the main channels to the powered subwoofer for monitoring. This does not affect the main mix tracks, which must include audio down to 20 Hz.

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 (see Fig. 1). 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.

Next; Back

Reprinted with permission from Magazine, November, 2000
© 2000, Intertec Publishing, A Primedia Company All Rights Reserved