Sound Reasoning: Recording Stereo Sound

Remember the last time you went to a movie and you heard the actors on the right side of the screen--and their voices came from the same side? Or you saw a monster stomp from one side of the screen to the other, and the sound of the footsteps moved through the theater?

That's stereo sound. And though it's not even available at most movie theaters, you can do it with a camcorder, provided you own the right equipment.

Webster's defines stereophonic as an adjective meaning "to render the illusion of true auditory perspective through the use of two or more mikes for recording." In more basic terms, it means breaking the audio signal into two parts--right and left--which, on playback, gives a more realistic sound.

Needless to say, any decent mike, whether it's built into your camcorder, attached as an external mike or connected to your VCR or audio recorder, should create a reasonable reproduction of the sound you're recording. But on playback, a mono (single-channel) recording loses the rich, spread-out sounds of a live classical orchestra, or the auditory positioning of the actors on a stage. When you think about it, a single source of audio is pretty limiting when things are happening all over your video screen.

The addition of stereo sound to your videos will provide the same illusion of perspective to the audio you hear that the video image does to what you see. But there's more to it than just sticking a stereo mike in the scene and hoping for the best.

In this article, we'll look at the various types of equipment involved in recording stereo audio. We'll consider the proper use and arrangement of different types of mikes to get the best stereo sound possible. We'll also note some of the problems in recording stereo that you might encounter along the way.

If your camcorder or VCR is limited to a single audio track, you cannot record true stereo. You could use any number of mikes connected to an audio mixer and this might give you a better representation of all the elements in the sound you record. But the final mix would have to be a mono signal to be compatible with your camcorder or VCR's single audio track. Even if you found a stereo audio tape recorder to record your stereo sound, it would be of little use if the video recorder you wanted to transfer it to had only a single audio track. The stereo effect would be lost at your camcorder or VCR as you shot or edited your tape.

For the purposes of this article, we'll assume that your camcorder or VCR has VHS hi-fi if you're using equipment in the VHS family, or AFM stereo if you're using 8mm gear. Both VHS hi-fi and 8mm AFM stereo provide both tracks necessary for good stereo recording.

Some industrial-level S-VHS decks offer dual linear audio tracks along with the VHS hi-fi. This gives you two ways to record stereo on one deck. Usually, the sound quality of these linear audio tracks is inferior to the hi-fi tracks, though considerably better than the single linear track on consumer VHS VCRs.

A few high-level Hi8 decks also offer PCM stereo audio along with the AFM stereo. PCM stereo offers near-CD quality sound--much better than the quality of AFM stereo. For a full explanation of these audio tracks, see "Camcorder Sounds" in the January 1995 issue of Videomaker.

Camcorders that have stereo audio generally come with a built-in stereo mike. This may seem a great advantage until it's realized that while shooting, the best placement for the camcorder and the best placement for the mike are seldom the same. Say, for example, that you're shooting a stage play. If you're shooting with a single camera, you'll want to be back in the audience where your lens can capture the whole stage. Here, your built-in stereo mike is as far from the talent as you are. Most theater halls deliberately have hard, bouncy acoustics to assist the talent in projecting their voices. That, combined with the distance to your mike, can muddle the sound by the time it reaches you and severely limit the stereo effect.

Fortunately for our purposes, most stereo camcorders have external stereo mike inputs. You can send signals from an external stereo mike, or several mike signals from a portable audio mixer, to your camcorder's external stereo mike input. These mikes can be placed anywhere you wish, regardless of the placement of your camcorder or VCR.

If your camcorder does not have an external stereo mike input, or has only a single audio channel, you can still get by if you have a stereo audio mixer and a VCR with stereo audio. You can run audio signals from the audio mixer to the VCR inputs while you run the video output of your camcorder to the video input on the VCR. The audio mixer is required because the audio inputs on your VCR require a much stronger signal (called a line-level signal) than a mike alone can provide.

If you use this method, you'll have to do the actual recording on your VCR instead of your camcorder. This requires carrying around a VCR to your shoots, and making sure A/C power is available. However, it offers you a chance to record stereo audio if your camcorder is not capable of recording or accepting external stereo mike signals.

The stereo mike input on most camcorders accepts a 1/8-inch mini stereo phone plug. A standard mono phone plug is made up of a tip and a sleeve (insulated from each other) to conduct the signal from a single mike into your camcorder, while a stereo phone plug has a tip, a ring and then the sleeve. On the stereo phone plug, the tip and ring conduct the separate stereo signals, while the sleeve acts as a common connection for both signals (see figure 1a).

The cable used with stereo mikes has two center conductors and a shield. At the camcorder end, the center conductors go to the tip and ring while the shield goes to the sleeve. At the mike end, the center conductors go to two separate mike elements while the shield goes to both mike elements and acts as a common ground. It's possible to divide this cable from your stereo mini jack into two mono cables should you wish to use two separate mikes rather than one stereo mike (see figure 1b).

This will also allow you to connect your camcorder to the outputs of a stereo or multi-channel mixer. Many good battery-powered portable mixers are available. It's always advisable to use a mixer if you're using two or more individual mikes to record stereo. When using a mixer, you have individual control of the level of each mike, allowing you to fine tune the balance of your stereo signal.

One major advantage here is that, unlike camcorders, most mixers provide a level meter for setting your separate audio levels. If you plan to connect a mixer directly to your camcorder's external stereo mike input, make sure the mixer offers mike-level outputs. Line-level outputs (with much stronger signals) will badly distort your audio if connected to your camcorder's external mike input. You use line-level signals only when you wish to connect a mixer's outputs directly to your VCR. Several good quality portable mixers offer both line- and mike-level outputs.