RICH TOZZOLI /
04.01.2012
Originally featured on BroadcastEngineering.com
5.1 bass management
Good management in the studio will maximize the surround experience at home.

Mixing 5.1 Surround Sound. Sure, it's a sexy term that invokes sonic visions of spaceship flyovers, car chases or front-row concert seats at Madison Square Garden. But, with the excitement and extra speakers comes certain challenges, such as bass management. We mixers must face the reality that much of our work will be heard on home theater speakers smaller than the palm of our hands, with the subwoofer doing most of the heavy lifting. With that in mind, let's explore how understanding bass management can help you produce and deliver a better mix.

Home-theater-in-a-box

Let's first put ourselves in the comfortable seat of the end consumer. Whether it is a multichannel TV broadcast, concert DVD or Blu-ray disc, our audio will most likely travel through one of the many home-theater-in-a-box (HTIB) systems available at local electronics giants. That means the setup will probably involve a 5.1 (or more) layout with Left Front (LF), Center (C), Right Front (RF), Left Surround (LS) and Right Surround (RS) speakers. Then, of course, there will be a subwoofer that carries the LFE channel, or the “.1” in the “5.1” term. (See Figure 1.)

These consumer speakers will be connected to the receiver, which will probably receive its input via digital output from a cable box, video game console or consumer player (such as DVD or Blu-ray). Unless it's full-range audio from a Blu-ray player, most consumers' receivers will take a Dolby (Digital) AC-3 stream, such as those sent by major TV broadcasts or movie channels.

That single stream is decoded (if encoded in 5.1) by the receiver, “broken out,” and sent to the appropriate speakers (L, C, R, LS, RS, LFE). But, the fact remains that these small home theater speakers often can't reproduce any bass information below 120Hz or so. That means bass management in the reciever will typically direct that information from each of the speakers down into the subwoofer. Combine that bass information with any of the LFE content from your mix, and you might have a big mess of low-end on your hands.

So, when mixing surround, I will “bass manage” my mix, either with hardware or software. This lets me approximate what the consumer will hear at home in a bass-managed home theater. While hardware systems are fine, I happen to rely on software — the Waves 360 Surround Tools package, specifically. I prefer software because of the recall ability, simplicity of setup and lack of additional cabling.

While the 360 bundle features surround reverbs, compressors and limiters, etc., the most important tool, in my book, is the M360 Surround Manager. This lets me calibrate the speakers and subwoofer in my room, adjust for various speaker angles and LFE settings and, in general, simulate the bass management of a home theater setup.

In the course of mixing, I will bypass the M360, which will then send full-range signals to the speakers. When activating the M360 (along with the LFE 360 plug-in), it will selectively filter the low end of each speaker (L, C, R, LS, RS) and send it into the subwoofer, along with my LFE signal.

Mixing the LFE channel

Let's talk further about mixing in LFE information. As the panner shows, there is a separate LFE fader. So, if this panner was assigned to the kick drum in a live-concert mix, raising that LFE fader would send some of the kick to the .1 channel, which would then be reproduced by the subwoofer. That applies to any channel with an LFE send — bass guitars, explosion effects, or even dialog or vocals from the center channel.

Taking it a step further, any mix information you send using an LFE fader will play back discretely in the subwoofer, both for you in the studio and the consumer at home. But, in a consumer's bass-managed playback system, the subwoofer will also playback any of the sub information cut off from the small satellite speakers in the receiver, along with your LFE information. In other words, be very careful when mixing the LFE channel. While it sounds good in studio to feel that sub rocking, all of that bass may overwhelm the consumer at home.

Before I understood how to use bass management, I made a mistake on a certain concert DVD. In the studio, I sent a lot of information from the bass guitar and kick drum to the LFE channel in the mix (which was not sent to mastering — hence, no “lifeguard”). So, when the DVD was released, consumers complained that the mixes were a bit too “muddy.” What happened was the above scenario had come true — where the entire low-end from the five speakers cut off in the consumer bass manager was sent to the subwoofer along with all of my LFE information from the mix. It was simply too much bass. If had used a bass manager, I would have heard the problem before it went out to the public. Needless to say, that never happened again. Now, when I mix, I use the LFE very sparingly, instead popping the bass manager in and out to simulate that consumer experience.

A good metering tool

Another important surround tool from the Waves 360 bundle that I rely on is the Durrough meter. (You can, of course, use any good metering tool.) Note that these meters are also available in hardware versions, which I've used quite a bit as well. What I do is watch channel 6 light up (where it's assigned in my 5.1 mix) when raising the LFE fader. Aside from hearing it through the subwoofer, I can see it go up accordingly on the meter as the LFE send is raised. Note that in a non-bass managed mix, the LFE channel will only light up when information is sent to it via the LFE fader. When checking with bass management “on,” channel 6 will light up on the meters even if no LFE information is sent. That proves that the bass manager is actually working — doing its job of sending audio that small speakers cannot reproduce (again, around 120Hz) to the subwoofer.

The use of bass management can help in many ways — the most important being the full understanding of what happens to the bass frequencies in a mix. By taking the time and effort to set up a bass management system, it can ensure that what you hear in your studio will be heard correctly at home.

Rich Tozzoli is a music producer, composer and mixer.



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