What Is Normal?
Back in the old days before FireWire, video producers had to capture audio through a separate input. This was messy sport. Video capture cards had their own audio hardware that often appeared to the computer as a second sound card, complete with its own level settings and adjustments. Capturing clean audio was a function of keeping the audio cables away from power supplies and RF sources and getting just enough volume, but not too much, lest you should overload the input. Today, it’s so simple to capture clean audio, right? Just plug in the FireWire cable and hit the record button. While improved Automatic Gain Circuits and digital capture have taken much of the guesswork out of video sound, most clips will benefit from normalizing.
Normalizing audio is pretty simple. First, select the clip you want, locate the find the Normalize function and select it. In Premiere Pro, right-click the clip on the timeline, select Audio Gain and then click the Normalize button. Of course, every editing package is different, but all the major players offer a similar function. The computer analyzes the audio clip to find the absolute loudest sound, and then adjusts the clip volume up to make the loudest portion 100% (but not more). This ensures every audio clip will play at the highest possible volume, which helps dialog stand out against background music and effects. Due to the volume of the person speaking, you may experience some rude volume shifts after normalizing multiple clips. If this happens, you have a couple of choices: either re-normalize the offending clips to a lower percentage or use the volume control on the timeline to adjust for a more natural sound.
Equalize and Stylize
Once your clips are normalized and consistent in volume, you may decide they need some additional help. This is a job for filters and equalizers. For instance, a High Pass filter allows sound above a given frequency to pass through, removing sound below the selected frequency. This is handy for eliminating low, rumbling sounds, like wind noise or mechanical vibrations. A Low Pass filter works in the other direction, allowing sounds below a certain frequency to pass while stripping sounds above that frequency. High Pass filters are great for removing hiss and other noises in the upper registers. Just don’t overdo it: you still want some crispness to the sound. Bandpass filters permit the middle portion of the audio spectrum through. Sort of a combination of high pass and low pass, the bandpass filter is great for simulating telephone calls, intercoms and portable radios.
Maybe you’d like more control than a simple filter can provide. If so, consider applying an equalizer to your audio clip. Essentially a sophisticated set of frequency filters, an equalizer may be as simple as the bass and treble controls on your car stereo or as complex as a 31-band graphic or parametric model. A graphic equalizer with just a handful of bands allows simple shaping of your sound. When using an equalizer, don’t fall into the trap of boosting everything. Listen closely to the clip and try reducing some bands first. Most of the time, you’ll find cutting frequencies is more effective than boosting everything else. Once you have the basic sound, try goosing the bottom end for some more authority or tweaking the high end for a little more sparkle. As with most things in life, a little moderation goes a long way.
Loud is Good
Even with Automatic Gain Control in the camera, your footage may still contain everything from a whisper to a scream. This range of volume can be frustrating to edit, but there are a couple of audio tools designed for this very purpose: the compressor and the limiter. An audio compressor simply reduces the difference between the loudest and the softest parts of your recording, otherwise known as the dynamic range. Compressor plug-ins come in many styles and designs, but most have three primary controls. Attack time is the amount of time before the compressor kicks in. Shorter times let the compressor react faster to spikes in volume while longer times ignore the transients and concentrate on overall volume. Release time determines how long the compressor waits before looking at the signal again. Short times respond quickly to changes while longer times even everything
out. Independent of attack and release is the compression ratio. This setting influences how aggressively the compressor squeezes the dynamic range of sound. Lower ratios gently smooth things while higher ratios force the dynamics to a minimum.
The limiter is like the compressor in many ways. A limiter places a ceiling on audio volume and won’t allow any spikes above a preset threshold. Limiters are great for reducing the peaks inherent in dialog and sound effects and will make your audio sound louder without affecting the overall dynamic range. Like compressors, there are several variations, but a basic peak limiter has a threshold setting to determine where volume is limited. Three decibels of reduction will make your audio sound roughly 50% louder while a six-decibel reduction makes it sound 100% louder. A peak limiter on your entire dialog mix flattens the volume spikes and keeps things more consistent. Compressors and limiters are often used together to even out the volume and make it punch through a dense soundtrack.
These tools are truly the fundamental sugars of audio sweetening. With some extra attention to your sound, combined with religious use of normalization and careful application of equalization and dynamics control, your projects will sparkle and punch with the best of them. To complete our cooking analogy, you’ll have a full meal with all the extras, minus the premium price.
Contributing editor Hal Robertson is a 25-year production veteran and owns a media consulting firm.
[Sidebar: Carpal Tunnel Reduction Strategy]
I recently edited a project that had what seemed like a million dialog edits. It wasn’t really that bad, but imagine trying to get all the clip properties (normalization, equalization and plug-ins) to match settings and volume. You could be clicking for hours. Here are a couple of tricks to reduce the strain on your wrist. First, when capturing dialog footage, try to capture longer clips that you’ll later divide into smaller chunks. Once on the timeline, but before slicing and dicing, apply normalization and effects first. This may seem backwards, but when you divide the clip into final edits, the audio adjustments will stay all the way through, reducing the amount of time required to unify all the clips. Second, many applications allow you to copy just the attributes of a clip and apply it to another clip (this might be on the right-click context menu of a Windows application). Finally, some editing applications (such as Vegas) have advanced audio editing capabilities, such as track-level effects that apply to all clips in a track, bus effects that apply to all tracks grouped in a mixer bus or even project-level effects.