FIG. 1: The LFE Send parameter copies the full-range signal to the LFE channel, which should then be lowpass filtered.
Surround production is not as mysterious as you might think. Everything you know about stereo (or mono) still holds true, but with more possibilities. There are new places to localize sounds, new ways to create space for an element, and new corners to paint yourself into. In this month's column, I'll look at both sides of the 5.1 coin (see “Step-by-Step Instructions” on p. 68).
Turn the center channel to your advantage by using it for sounds that you want to stand out or be tightly localized. A part that comes primarily or exclusively from the center channel is essentially mono: its timbre and position are the same from any seat in the house. Beware, however, that if you place your lead vocal only in the center, a listener could mute the center channel and create instant karaoke.
Phantom center is not dead, though. In film, sounds that occur center stage behind the actors exist only in phantom center — not in the center channel. In Digidesign Pro Tools 7, a control called Center Percentage moves center-panned sounds between only the center channel at one extreme and the left and right channels at the other. You can use that to achieve any blend of discrete and phantom center. In Cakewalk Sonar 6, phantom center in a surround project requires assigning the track output to a stereo bus and then assigning that bus to the surround output.
Your Other Left
Theoretically, you can create a stereo field between any pair of channels in a surround setup. In practice, having ears on the sides of your head limits (but does not eliminate) your ability to localize between front-to-back or diagonal pairs. That still leaves plenty of room for experimentation with L/C, C/R, and Ls/Rs stereo, not to mention good old L/R.
Web Clip 1 demonstrates this technique, spreading a drum kit across the L/C stereo field, bass and keyboards across C/R, and strings across Ls/Rs. This is a natural-sounding way to take advantage of the extra real estate that surround sound affords. It builds on tried-and-true stereo-panning techniques while removing the need for all the stereo kludges invented to deal with a crowded soundstage.
On the Down Low
The LFE channel should be used sparingly, because in too many circumstances — Dolby Digital down-mixing, for example — it is compromised or eliminated. In music production, the LFE is usually used to add thump and punch to kick drums and low bass notes. Keep in mind that bass management in the listener's playback system will take care of shifting the low end of each surround channel to the subwoofer, so you needn't use the LFE for that. (For more on bass management, see “Square One: How Low Can You Go?” in the February 2006 issue of EM, available at www.emusician.com.)
Sonar's surround panner includes an LFE Send parameter (see Fig. 1), which copies the signal (the way that any send does) and sends it to the LFE channel. Note that this is a full-range copy, whereas the LFE is designed for only the bottom couple of octaves. If you were to connect your LFE output directly to a subwoofer, it would try to play back the entire signal, with bad results. Although some surround sound monitor controllers filter the LFE, you should do it yourself to be sure that you bounce a filtered LFE.
Insert a Sonitus:fx EQ on the main surround output bus. Because it's not a surround effect, it will load using SurroundBridge. Unlink the LFE processor and bypass the rest. On the LFE EQ, disable four bands and set the other two to Lowpass, with a 90 Hz cutoff and a 1.5 Q. The serial filters increase the effective slope without creating a resonant peak. I set the cutoff at 90 Hz, making the 3 dB down point approximately 80 Hz, which is more or less the standard.
Because most listeners will hear your mix on a bass-managed system, it's important that you check your mix with bass management to listen for any phasing problems it may introduce. Sonar makes this simple, with a checkbox in the Surround tab of Project Options. Check out Web Clip 2 for instructions and an example for doing the same thing in Pro Tools.
Now all that's left is to deliver your mix. Know which surround sound format your client needs. For a DVD, which requires Dolby Digital and supports DTS, bounce multimono (not interleaved multichannel) Broadcast Wave files and bring them into an encoder such as Apple's QuickTime Pro or one of Minnetonka's SurCode products. For Web distribution, Sonar can export directly to Windows Media Professional.
Brian Smithers is course director of audio workstations at Full Sail Real World Education and the author of Mixing in Pro Tools: Skill Pack (Thomson Learning, 2006).
Use discrete center-channel signals to emphasize important parts and L/R phantom images for secondary parts.
Use L/C, C/R, and Ls/Rs (shown) stereo fields to set the stage.
Use LFE sparingly. Your mix should be able to survive without it.
Lowpass-filter the LFE channel steeply; the signal should be 3 dB down at 80 Hz.
Check your mix with bass management.
Know the proper delivery format, such as WindowsMedia Professional for Web delivery or multimono PCM to be encoded to Dolby Digital.