Sound Advice: Stereo Mix-O-Phonic Sound

Remember records? Maybe I’m giving away my age, but I spent countless hours as a teenager dropping a tiny diamond stylus into those marvelous vinyl grooves to hear my favorite artists and songs again and again. As much as I enjoyed the sound, half of the fun was reading the backs of the album jackets. Words like Stere-O-Rama and Multi-Phonic sounded mysterious, like some kind of secret language shared with the public, but understood by only the privileged few in the recording industry. Of course, as an adult, I realize that those enigmatic words were just marketing jargon for a process we call stereo today. While the mystery of the words is gone, stereo remains a mystery for many video producers. Why even bother with stereo? Won’t most people just listen to your finished video on a tiny TV speaker? Why go to the trouble? Learning to create an interesting stereo soundtrack is time well spent on the quality of your video. A stereo mix puts your video in a completely different category.

During The Shoot
While most of your stereo creativity will come in the post-production process, there are several things you can do during the shoot to help create the stereo sound. The first thing is to record in stereo. No, this doesn’t mean using your camcorder’s built-in stereo microphone. To get a good stereo recording, you need external microphones, a mixer and all the associated cables, stands and adapters. This is quite a lot of extra trouble and equipment, but your listeners will notice the difference. A Spring band or choir concert is an excellent opportunity to capture stereo sound. You’ll need a tall microphone stand to place above and just behind the conductor. On top of the microphone stand, you’ll mount two matched directional microphones. Using a microphone technique called XY Stereo, install the mikes with their capsules overlapping and exactly 90-degrees opposite each other. This stereo technique ensures a nice stereo sound image and reliable mono compatibility for those listening on single TV speakers. Alternatively, you could choose a stereo microphone. Several are available and most use the XY Stereo technique inside a single mike body. This simplifies installation and minimizes the visual impact of the microphone.

Another way to use stereo during the shoot is to capture ambient sound beds to incorporate in your finished video. Let’s say you’re shooting an interview and there is a unique sound signature at the location. Maybe it’s birds in the trees, the clinking of utensils in a restaurant or the roar of traffic in the background. After the interview, set up your stereo microphone and record a few minutes of the sound. Later, during post-production, you can use that ambient sound bed to create atmosphere or to help seam together two different-sounding takes in the interview. Vocals, even in music but especially for narration or interviews, is often monophonic anyhow, so the ambient stereo atmosphere is all you’ll need to provide depth in your production.

Post Tricks
Virtually every movie and television show enhances their stereo sound in post-production. Most of them simply create the whole sound track from scratch in post. The punches, footsteps, gunshots, rustles of clothing and cell phone rings you hear are often recorded in a studio and placed in the stereo mix after the fact. You can leverage the audio capabilities of your video editing application to create many of these same stereo effects. All the major editing programs have mixing facilities for arranging various sounds in the stereo sound stage.

While most of your dialog segments will be anchored to the center of the stereo spread (i.e. balanced left and right or monophonic), you can be a little more creative with other elements of the production. For instance, a telephone rings during one scene. Where is the phone? On-camera or off-camera? Using the pan adjustment on a separate sound effects audio track, move the slider, knob or rubber band for the phone ring until it sounds like it’s coming from the physical location of the phone, whether that phone actually exists in the real world or not. You can indicate an off-screen phone that’s never seen by simply panning hard left or right and reducing the volume a bit to simulate the distance from the screen action. Use the same technique for other sounds in your video, making sure their pan position matches their physical location. Pay special attention to video cuts that change the perspective of the viewer. Your stereo mix must change immediately to reflect this camera movement.

Another stereo mixing technique is continuous panning. This method takes a sound and moves it — slowly or quickly — from one side of the screen to the other. Obvious examples are vehicles racing past a fixed shot and subjects walking across the screen, with their associated sounds. Other illustrations include bullets or arrows whizzing by and people, or other objects flying across the screen and falling or crashing into things. Now you can have some real fun. Using the same controls you used for panning the phone ring, continuous panning involves a starting and ending point for the sound. Some applications use key framing (via pan envelopes or rubber bands) for their audio controls on the timeline to achieve panning. Some software editors even record your manipulation of the panning sliders while you preview the project and then automate the pan on the timeline. In any case, you’ll watch the scene over and over again to get the panning just right. When you’ve nailed it, the sound will follow the action and the viewer will be drawn further into your production.

As nice as it is, all is not peaches and cream in the stereo world and there are pitfalls you should learn to avoid as you produce your soundtracks. The most devastating problem is phase cancellation. If, during the capture segment, or even during post-production, the phase of one of the stereo channels becomes inverted 180-degrees, all of your mono content will disappear when played on a single monophonic TV speaker. Causes include simple things like mis-wired balanced cables and adapters or something as simple as clicking the phase invert button in your audio editing application. It is easy to mis-phase cancellation on a stereo playback system, such as your editing bay: the audio may be indistinct or unfocused or it may even change volume dramatically as you move your head around between the speakers, but you’ll still hear it all. That’s why it’s important to preview your stereo projects on a monophonic system, preferably the crummy little TV in the back bedroom or garage. If your project looks and sounds good in this environment, you can be confident it will stand up in most others.

Yes, it’s more trouble to create a good stereo soundtrack. In fact, it is probably a magnitude harder, instead of only being twice as hard as a monophonic mix. But there are additional creative outlets in mixing stereo sound and your audience will enjoy and respond to the audio in a positive way. It’s not for every video, but the next time you build a project, consider how stereo sound would make a better video. Plus, you can put some cool word like Spectr-O-Sonic Sound on the cover.

Author Hal Robertson has been producing stereo soundtracks for over 24 years. He owns a consulting company that specializes in media production.

[Sidebar: Mixmaster]
Want the short list? Here are four simple things you can do to improve your stereo mixes.

1. Get It Right the First Time. Before and during the shoot, make sure you record a clean, loud signal and that your cables and equipment are in perfect working order.

2. Mix It Right. Listen closely to make sure your stereo elements don’t overpower dialog.

3. Don’t Go Crazy. Make smaller adjustments in panning (and volume) for subtle effect. 30% left or right is often all you’ll need for on-screen audio elements.

4. Reality Check. Listen to the finished video on another system to ensure mono compatibility.

The Videomaker Editors are dedicated to bringing you the information you need to produce and share better video.

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