Sound Track: The Whole Truth

by Loren Alldrin
November 1998

Kara pulled an all-nighter editing a year's worth of memories for her company's New Year's eve party. When it came time to play the video on the company's projection TV system, Kara experienced a ru de awakening--nothing sounded right. Voices that seemed clear when she edited were garbled and indistinct. Her music, routed to tape through an inexpensive mixer, was nearly drowned out by a loud hum. Her husband's voiceover commentary came booming out of the speakers at an uncomfortable level. Worst of all, the CEO's congratulatory speech sounded so bad that it prompted chuckles from several of Kara's co-workers.

What Went Wrong?
Kara learned the hard way that it is extremely important to have trustworthy speakers when you are making crucial decisions about your audio. Kara trusted the tiny speaker from her $150 TV. Instead of telling her the truth about her soundtrack, it obscured the details she needed to make good decisions about relative levels, equalization and the like.
There are two main performance factors that separate good speakers from bad: breadth and uniformity of frequency response. Breadth quantifies how high and low in frequency a given speaker will go. The human hearing range covers the span from about 20 Hertz (Hz, or cycles per second) to 20,000Hz (figure 1). The closer a speaker comes to covering this full range, the better. Frequency response is one of the few speaker specifications manufacturers commonly print.
Even more important, however, is the uniformity or smoothness of a speaker's response. If a speaker puts out a lot more volume in a certain band of frequencies, sounds that occupy this area will appear louder on playback than they really are (figure 2). If a speaker has a peak in the human voice range (which sits right in the middle of the spectrum), you may think you've mixed your narrator plenty loud above a music bed. Play your tape back on a truly "flat" system, however, and you may discover that his voice is actually buried in the music. Unless a manufacturer prints a frequency response chart, there's no way to know how smooth and even a speaker's response is without listening to it.
In this column, we're going to check out some of the more popular monitoring options used by videographers. And while performance can vary wildly within a given class of speaker, there are generalizations we can make. Some of the monitoring options we'll discuss are as trustworthy and reliable as an old friend, others are veritable masters of deception.

Tiny Monitor Speakers
Expensive video monitors and cheap TVs have one thing in common: they often contain notoriously unreliable speakers. Tacked on almost as an afterthought, these speakers aren't much larger than those found in full-size headphones. This is the type of speaker that helped Kara botch her soundtrack.
These speakers are so bad because their frequency response is both limited and very uneven. Their limited range means they'll completely ignore moderately low and high frequency sounds. A low 60Hz hum from a power cable might be completely inaudible when listening on a tiny speaker, as would large quantities of high-frequency tape hiss. These little speakers rarely even cover the human voice range--they may be cutting off fullness on the bottom end and clarity on the top.
Little speakers don't perform so well in the evenness area, either. Their response is usually riddled with peaks and dips, imperfections that make it impossible to perform critical adjustments to your audio. These speakers are good for making sure you actually have audio on tape, but that's about it.

Standard TV Speakers
Standard television or A/V monitor speakers are better. These are usually larger and cover a broader range of frequencies than cheap monitor speakers. These speakers often do justice to the human voice, and may reproduce music with reasonable fidelity. Response is usually smoother than with smaller speakers, though a buildup of the lower mid-range frequencies is common.
Because many televisions use speakers firing out from the side of the cabinet, sound can be a little lacking in the more-directional traveling high frequencies. One solution is to secure flaps at a 45-degree angle over the speakers to direct the sound forward.
More and more TVs include stereo speakers as well. These will allow you to hear both left and right channels of audio at the same time, but don't really offer the accuracy required for critical stereo production.

Multimedia Speakers
Multimedia speakers, like those included with many computer sound cards, offer widely varying performance. Some sound as bad as tiny monitor speakers, while others offer accuracy more on-par with large television speakers. Most multimedia speakers are far too small to generate much bass, but some do offer good high-frequency reproduction. The exceptions are those self-powered systems that include subwoofers, which generate more than enough bass for video production.
Though they offer the advantage of pointing right at you, the response of most multimedia speakers is pretty uneven. Unless you're reasonably certain your multimedia speakers are giving you a true picture of your sound, you may want to leave them attached to your computer.

Portable Stereo Speakers
The "boombox" represents one of the best audio monitoring options for the videographer on a budget. Systems with larger, detachable speakers usually offer fidelity far better than that of even an expensive television. You can position the speakers for optimum sound and stereo imaging, placing the main part of the stereo in a convenient location. Portable stereos have built-in amplifiers, and many have built-in equalizers that can help overcome limitations in the speakers' response.
Portable stereos usually have pretty broad responses, with a tendency toward hyped bass and treble output. If a boombox sounds very rumbly on the bottom end or too "fizzy" on top, it may not be the best choice for video monitoring. Try to find a model with a clearer sound.

Small Bookshelf Speakers
Small home stereo speakers usually offer good fidelity from a very compact box. These speakers are often two-way designs, with separate drivers handling bass and treble frequencies (figure 3). If you have an amplifier sitting around (or can attach these to a television's external speaker jacks), these speakers are a great solution for video production. Self-powered systems with a subwoofer also work well.
Related to these speakers are the small audio monitors designed specifically for video and multimedia production. Usually magnetically shielded so they don't bother your video monitors, these speakers are even more trustworthy than home stereo speakers.

Large Home Stereo Speakers
Though these may offer the best fidelity of all your options, most people just don't have the room for large home stereo speakers. Cramped quarters often mean putting these big speakers against a wall, where they rarely sound their best. Many inexpensive full-size speakers also have an accentuated "boom and sizzle" response that makes them a questionable choice for video.

Headphones
Like every other monitoring option, headphones run the gamut from excellent to truly horrible. Larger, more expensive headphones are usually the most accurate. Designs that cover the ear are the best choice of all.
Though they're far better than relying on a lousy speaker when editing audio, headphones have a hidden danger: they can sound too good. The ultra-detailed sound of many headphones can trick you into thinking your audio sounds better than it does. Remember that most people won't be watching your video with headphones on, so be careful when relying entirely on phones for production. For tracking down problems with your audio, however, headphones can't be beat.

Last-minute Advice
In closing, here are some tips for getting the best sound out of any monitoring system:
1) The poorer-sounding or noisier a room is, the closer you should be to your speakers. Just as when you're recording audio with a mike, this will help minimize competing noises and unwanted room ambience. Got a really bad monitoring environment? Use headphones.
2) If you have equalization for your speakers, listen to some favorite music and adjust the EQ until it sounds right. This will "calibrate" your speakers for optimum accuracy.
3) Don't place speakers right against a wall. This causes a buildup of bass and mid-bass frequencies, potentially making everything sound muddy and dark. Pull speakers out at least 18 inches from the nearest wall, if possible.
4) Position stereo speakers so the left speaker, right speaker and your head are at the corners of an equilateral triangle. In other words, you want the same distance between the speakers as between your ears and each speaker (figure 4).
5) When you think your soundtrack is perfect, listen to your tape on as many other audio systems as possible. Each will give you a different perspective on your audio.
Good luck!

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