After years of stereo mixing, mixing for surround can be a creative challenge.

By the end of the last century, recording engineers had pretty much figured out how to mix music for stereo playback. We knew what worked. We knew where things should be panned. We had a good grasp of what types of speakers people were listening to. We knew, generally, how people set up stereo speakers in their homes. Stereo mixing and stereo playback was a done deal. With the advent of surround sound, be it for movies or music, everything we knew has gone out the window. In these still early days of mixing for surround, there seem to be no rules, no set-in-stone standards. There are as many approaches to a mix as there are engineers.

Let's take a look at what challenges 5.1 creates in the studio. How does it differ from mixing in stereo? Why is mixing for the movie theater different from mixing for home playback? What works and what doesn't? To get a better understanding of the intricacies of some mixes, it might be time to start experimenting! I know I'm not the only listener who unplugs speakers so I can hear exactly what an engineer is doing and what is going on in a particular channel — we all do it, right?

For the most part, we'll use music as our source, because it causes the most problems for mixers, and also opens up a world of new opportunities. Movie sound effects are typically tied to the picture — if something is making a noise on screen right, then that's where the sound effect must be placed. Dialogue is almost always in the center channel. A space ship flies in from behind the camera across to the front left side of the screen, and the sound must do the same. However, anything is possible in a music mix.

How is mixing in 5.1 different from mixing for stereo?
Ah, the simple joys of a stereo music mix. Vocals dead center. Reverb panned hard left and right. Kick, bass and snare also securely in the center. The tom-toms spread across the stereo panorama, hi-hat hard right. The other instruments scattered across the soundstage, so if you close your eyes, you can point to where each player was onstage. The audience in a live recording is also panned to the full stereo width, hard left and hard right. If it is a classical recording, it's even simpler. Each instrument is placed exactly where they would appear on stage — violins on the left, cellos on the right, and so on.

A typical surround setup (left) has 5 speakers and a subwoofer, compared to a two-channel stereo setup (right). All those extra speakers and that enveloping sound mean that a 5.1-channel source gets mixed differently than a 2-channel source.

Now, don't think for an instant that this makes mixing completely simple. Because the sounds are coming from just two speakers, room has to be made in the mix for each instrument. Frequencies play a great role. The engineer has to make sure that each instrument occupies a unique sonic space, to differentiate it from all the other instruments coming out of those two speakers.

Also, on the plus side, quite a lot can be hidden in a stereo mix. The perceptual concept of masking plays a big role here. If there is some noise on a track, some distortion, and even some tuning issues, these can be covered up by everything else blending into the two channels of a stereo mix.

Now, consider what happens when that mix, with each of those little indiscretions, is spread out across six speakers. In a stereo mix, a background vocal that was slightly out of tune caused a nice chorusing effect in the stereo mix. Now, that vocal part is sitting by itself in a surround channel, noticeably off pitch. Or, the amplifier noise on a guitar track (that was masked under the rest of the band in the stereo mix) is humming away all alone in the other surround channel.

There is another problem that is encountered frequently. Whenever I start a session, I always ask the producer where this mix will be played. Is it for playback in a theater? Is it strictly being played over a television set? A huge ballroom? Knowing this helps me determine what to mix for and what speakers to use to monitor my mix, either large or small. With a DVD release, the engineers never know if it's going to be played over a custom-tuned, THX-approved $80,000 home theater or over a $250 home-theater-in-a-box. While this has always been an issue with a stereo mix, the number of speakers in a 5.1 setup multiplies the complexity.