Got Ya Surrounded
Dec 1, 2006 12:00 PM, By Steve Kutay
As the number of households with home-theater systems continues to grow, more and more artists are releasing versions of their music for the 5.1 or 6.1 surround-sound formats. After first being popularized by audiophiles for classic standbys such as Dark Side of the Moon, contemporary artists are using this medium to further explore and enhance the music-listening experience. The Crystal Method, LTJ Bukem, John Mayer, BT and Cornelius are a handful of artists who have made the leap into surround. Whether or not to mix in surround requires consideration because there is a financial and intellectual commitment involved. First and foremost, will your style of music benefit from additional channels? If so, will it be worth the extra effort and expense?
There are two primary motivations for mixing music in surround: acoustic realism (the more common use so far) and musical effect. A frequently used method of surround-music mixing places the listener within a controlled acoustic environment. Theoretically, a surround mix can force a variety of listening perspectives: anywhere from the rear row of an auditorium to a spot onstage between the bass and the drums. In reality, more intense perspectives only diminish or confuse the listening experience. Nonetheless, the creative potential is huge. A more conservative placement within the audience can be greatly enhanced through the use of surround-capable reverb plug-ins available on the market. For example, Audioease Altiverb (price varies; www.audioease.com) features a wide array of modeled environments, from the Sydney Opera House to the interior of a Volkswagen Beetle.
The less explored avenue for surround-sound mixing involves using the additional channels to present musical ideas. That may be impractical for many genres, but it's more than acceptable within the urban, electronic and dance idioms, where pushing the boundaries of the listening experience is common. With six or seven discrete channels, you can creatively use the additional acoustic space and redefine musical relationships. Parts may be assigned spatially or moved across the surround plane, and reverbs and delays may be panned anywhere within a 360-degree radius. With a dedicated subwoofer, ground-shaking lows may be more accurately reproduced in a surround-sound setup. Without some discretion, however, you risk ranking style over substance. It's still about the music. The surround perspective should enhance musical relationships, not replace them, so exercise taste when mixing.
BUILD THE WALL OF SOUND
Depending on how your studio is set up, whether it's primarily digital or hardware based, you will need some or all of the following: surround plug-ins, multichannel soundcard, bass-management software or hardware, a 5.1 speaker system (five matched satellite speakers with a subwoofer), a surround controller and a surround encoder. Don't underestimate the importance of having matched satellite speakers. Conveniently mixing different speakers to complete a surround system will cause big headaches when you monitor your mix because different speakers have different frequency responses. Select reliable speakers with a flat response.
The International Telecommunications Union (ITU) created a widely accepted standard for speaker placement for 5.1 systems (see Fig.1) that involves placing the speakers along the circumference of an imaginary circle. The center (front) speaker is located straight ahead at 0 degrees, with the left front speaker at -30 degrees and the right front speaker at +30 degrees. Left, center and right speakers should now be equidistant from the primary listening position. The left surround (rear) and right surround (rear) should occupy the positions of -110 degrees and +110 degrees, respectively. Given your specific studio size and setup, it may be difficult to place the surround speakers at ±110 degrees. A tolerance level of ±10 degrees is acceptable. If mixing for 6.1, place the center surround speaker at 180 degrees. Because the subwoofer is omnidirectional, placement is not as critical; however, it is suggested that you start by placing it to the right or left of the front speakers. Your room will influence the reproduction of bass, so you should consider experimenting with the subwoofer location to eliminate any excess boom from standing waves and locate the position that gives the smoothest, most natural response.
FINDING THE BALANCE
Before calibrating your speakers, it is important to understand the complete function of the subwoofer, since you will need to keep these functions in mind when calibrating. Though sometimes misconstrued, the Low Frequency Effects (LFE) channel and the Sub signal are two distinct signals that are output by the subwoofer unit. Originally created for dramatic sound effects for film, the LFE, or .1, channel is a discrete channel for low-frequency content, while the Sub signal is composed of redirected low frequencies from the satellite speakers. Through a process called bass management, a crossover frequency is applied to filter out low frequencies from the satellites to be summed and fed to the subwoofer unit. Most home-theater systems employ bass management, so it is important that you monitor your mixes with a bass-management system applied. When printing your mix, however, be sure to bypass your bass management because this process will be performed during consumer playback.
To calibrate your speakers, you will need a sound-pressure level (SPL) meter or spectrum analyzer. Fortunately, Radio Shack offers such meters at a low cost. In addition, you will need a pink-noise source. Different studio setups and equipment may have specific instructions for calibrating. It is important that you consult both hardware and software manuals prior to calibration. For now, here is the basic process.
Begin by selecting a fixed reference level, somewhere between 79 and 82 dB, which is the recommended reference range for music. For the purpose of this article, I'll use 80 dB. Turn on your meter and set it to “C” weight using a slow scale. Either hold the meter chest high away from the body or place it on an adjustable stand, such as a folding music stand, so that the microphone is in the prime listening position facing up between the cones of the center speaker at a 30- to 45-degree angle. It is important that the listening position is free of anything that may reflect additional sound toward the mic. Now solo your center speaker and play the pink noise. You will notice the measurement oscillate due to the varying peaks it is reading. Wait for a few moments to determine the average reading, and then adjust the level on the speaker or the pots on your I/O or surround controller until you get 80 dB. Repeat this process without moving the meter for the left front and right front speakers, measuring each speaker individually. To measure the left and right surrounds, rotate the meter to -90 degrees for the left surround and +90 degrees for the right. If you are working in a small room with near-field monitors, it may be necessary to reduce the surrounds by 2 dB or more.
To calibrate the Sub/LFE, you will need to take two measurements. First is the Sub, which sums the low frequencies of the satellites during bass management. Consult your bass-management software or hardware manuals because they may have specific guidelines for calibration. With all satellite speakers turned off, send the pink-noise signal through the center speaker. If you're using bass-management software, you may be able to leave the center unmuted and solo the subwoofer. You will now hear the signal from the subwoofer being produced within a range of approximately 20 to 120 Hz. Set the “send to sub” level to 6 dB less than the reference level of the other speakers (in this case, 74 dB). Repeat this process for the remaining satellite speakers.
To set the LFE channel, mute all the speakers and subwoofer sends. Now send the pink-noise signal to the LFE channel and adjust the level to 4 dB higher than the satellite reference level (in this case, 84 dB). After that, calibration is complete.
THINK BEFORE YOU MIX
Over the years, different surround requirements have produced different track layout standards (see Fig. 2). The three most commonly used standards for 5.1 surround track order include SMPTE/ITU, Film/Pro Tools default and DTS. Most multitrack software allows you to reorder your tracks from a default setting if a separate standard is desired.
With more channels at your disposal, defining the spatial image becomes exponentially more complex. At the base level, you may want to set static pan positions and then leave them alone. Without extra consideration, however, you risk creating a mix that is somewhat less than what you may have intended. With some tasteful dynamic panning, you can really bring your compositions to life with sounds moving across the surround field. In addition, divergence is an adjustable attribute that allows you to assign content discretely to one speaker or spread the signal over adjacent speakers for a more immersive quality. Experimentation is the key.
Another thing to consider is that some consumer systems do not support surround sound. For that reason, you must fold your mix (downmix) to be certain that your mix will translate properly in stereo. Surround software and hardware controllers allow for easy downmix comparisons.
Once you've arrived at a satisfactory mix, you'll want to test it in a home-theater environment. Your files will need to undergo an encoding process that compresses the data, reducing its size on the disc, which will be decoded during playback. Almost all home-theater systems today contain, among others, Dolby and DTS decoders. There are a number of software encoders on the market that support encoding for DVD and CD. One of the easiest and cheapest solutions is SurCode CD-DTS ($99; www.surcode.com). Once encoded, simply burn to a CD using any audio CD burning software.
The world of surround is one of changing trends and developing technologies. If you have the interest and commitment, further study is essential because this article is a brief overview of mixing in surround. For reference, I recommend exploring the resources at SurroundAssociates.com, Dolby.com and DTSonline.com. For an in-depth technical read, try the book 5.1 Surround Sound Up and Running (Focal Press, 1999) by Tomlinson Holman. With knowledge, patience and experimentation, you will be well equipped to express yourself in surround.
CYCING '74 UPMIX
Nothing can replace the care and attention to detail that goes into a good surround mix. But if time is an issue, you may want to consider adding the UpMix software suite ($495; www.cycling74.com) to your arsenal of surround tools.
UpMix, the centerpiece of this surround package, uses a variety of algorithms to convert stereo or mono material into a full, immersive 5.1 surround track. There's also Rotator, which provides quick and easy image rotation of the five main channels of a complete 5.1 mix; ReRoute, a utility designed to reformat the surround track order to meet any 5.1 channel layout; FoldDown, which allows the user to test surround mixes in stereo and offers center and rear attenuation adjustments; LFE-6chan, which creates or modifies the LFE track with gate, downshift and oscillator functions; and ReBalance, a stand-alone set of faders for level adjustment of each of the 6 channels.
On the whole, the UpMix suite is a handy set of tools for the surround mixer. Though not as rich as some other surround applications, it does succeed at speeding up surround tasks and does so at a lower price. But what sets UpMix apart is the creative element it can add to surround tracks. Sure, you can take your stereo music into surround by quickly adjusting presets, but it also has the ability to shape and color the tracks in ways you may not anticipate. The UpMix plug-in is, however, content dependent, and the style and richness of your track will play a role in how it translates. Ambient and transparent tracks are the most malleable over the whole spectrum of algorithms. In fact, you may want to apply the UpMix processing to individual parts within a surround mix for added color and depth.
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