You're Surrounded
Page 1, 2, 3, 4, 5, 6
Let’s apply this concept to bass management. Suppose you have five NS-10 speakers and a big subwoofer that reproduces only the LFE channel (explosions and such). Each speaker directly monitors a final output track. The NS-10 has a small woofer in a small cabinet, so it naturally rolls off anything below 60 Hz or so. If your source tracks have any sonic material with extra bass in the 20 to 40 Hz region, you’ll never hear it on these monitors.
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FIG.
4: Although the subwoofer handles the bulk of low-frequency (below
80 Hz) chores, you still need to feed full-bandwidth audio to the
other five channels. The bass-management filter shown here affects
only your monitor system; the recorded L, R, C, Ls, and Rs channels
still contain the entire, unfiltered signal. |
Many mixing engineers think bass management has something to do with filtering the signal before it goes to the final mix-tape tracks. That’s simply incorrect. In fact, each of the L, R, C, Ls, and Rs channels should get the full 20 Hz to 20 kHz program signal. You don’t want to reroute the lows in these channels to the LFE channel; that’s what the bass-management filter in the playback system is for. Instead, you want a bass-management filter in your monitoring system that emulates the home-theater playback system (see Fig. 4). This filter is placed after the mixing tape deck and directly feeds the monitor amplifiers, as shown in Fig. 1. If you’re using a home-theater receiver for monitoring, it has an integral bass-management circuit, which does the job just fine.
Another misconception is that you must match the 80 or 120 Hz bass-management cutoff points in home systems to properly monitor in 5.1 surround. But because this filter is for playback and monitoring in your studio only, you have to do just what is needed to extend the low-frequency capability of your own monitoring system. Just as we don’t care about the crossover frequency of the midrange driver in a home speaker, we don’t know and don’t care about what the exact bass-management frequency is in a consumer system. We just know that somewhere around 100 Hz, all the bass energy will head to the big subwoofer cabinet.
My main monitors go down to 35 Hz, so I like to adjust my bass-management cutoff frequency down to 50 or even 40 Hz. This would limit the bass-localization effect (yes, you can localize 80 Hz bass, contrary to popular belief) and take some of the power load off the subwoofer, which attempts to reproduce the bass from the five main channels as well as the LFE information. That’s why you should buy the largest subwoofer you can afford and fit in your studio. For excellent information on bass management, download Steve Harvey’s paper Secrets of Doing Surround Sound on Your Existing Console, published by Martinsound (www. martinsound.com/ lb_rp.htm).
Alas, there’s no inexpensive way to put a separate speaker controller with bass management into a small studio. Martinsound makes something called the MultiMax controller, which does all the calibration, downmixing, and level control you could want, along with rudimentary bass management. (Downmixing refers to creating a stereo mix from a 5.1-surround mix.) It’s certainly a great controller, and I take one along on my surround seminars because it’s easy to use under stress. But its price of $3,000 is beyond many small-studio budgets.
Studio Technologies makes the Model 68/69 StudioComm ($1,599), which can be combined with the Model 65 Bass Management Controller ($899) to provide a $2,500 solution. These seem like expensive pieces of gear until you start shopping and find devices offering basic functions for up to $15,000. Gaaaaa! What’s a personal-studio owner to do?
Using a home-theater receiver starts to look better all the time, because it handles bass management and speaker calibration, it decodes DTS and Dolby Digital discs, and it gives you a big knob that changes the levels of all channels at once. (Remember, you also want a receiver that includes six analog inputs that bypass the decoders so you can monitor the 6-channel mix directly.)
You could combine something like a Yamaha RV-1105 receiver ($700) with five small monitors and a self-powered subwoofer for an affordable speaker/amp/bass-management/calibration system.
Even if your console has only stereo outputs and some extra auxiliary sends, you can get into the surround-mixing game. Of course, doing fancy spins around the five main speakers is challenging, if not impossible, without a true surround panner that employs a joystick or mouse. But some of my first experiments with static surround mixes were done with limited tools.
For instance, on a console without subgroups, if you have four extra aux outputs, you can patch the stereo bus to the front left and right channels, aux 1 to the center channel, aux 2 to the LFE channel, aux 3 to the left surround, and aux 4 to the right surround. (Of course, if your console has only four aux sends, this leaves you no way to easily add effects.) The LFE output should be sent through a lowpass filter with the cutoff set somewhere around 80 Hz so that the LFE information is completely out at the 125 Hz “speed limit.” This patching works fine for static mixes, such as symphonies, in which you’re only setting the relative levels in each channel for the duration of the track.
Getting an audio source to pan across the sound field takes a few tricks with subgroups. On a console with at least four subgroups, you can assign buses 1 and 4 to the front left and right channels, bus 2 to the left rear, and bus 3 to the right rear. Patch separate aux buses for the center and LFE channels.
Now, by panning between odd and even buses, you can perform front-to-back moves in the surround sound field. Also, by selecting a combination of buses, such as 1, 2, and 4, you can even manage a diagonal pan. This system can work out quite well with consoles that have pan and subgroup automation.
Reprinted with
permission from 
Magazine, November, 2000
© 2000, Intertec Publishing, A Primedia Company All Rights Reserved