Have you ever wished the dialog in your videos were a little less muddy? How about that music track that needs a smidgen more zing to make it cut through the mix?</P
Whether you need subtle improvements or more drastic corrections, these common problems both require some audio equalization or EQ. Equalization is often misunderstood, or worse, ignored by many video editors. The basics are pretty simple, once you understand the tools, the results can transform your video sound from acceptable to incredible. You already have everything you need, so let's learn to use it for maximum impact.
Audio Spectrum 101
Sound, as it reaches our microphones and ears, is a product of volume and frequency. Volume is easy — it's loud, soft or somewhere in-between. Frequency, however, is a bit more complicated. Measured in Hertz (abbreviated Hz), the sounds we hear are a combination of air vibrations at various frequencies or cycles-per-second. The lowest are around 20Hz, while the highest sounds are about 20,000Hz. With musical instruments as an example, think of a very low note produced by a pipe organ. This could easily approach the lower limit of our hearing. On the upper end of the scale, imagine the sound of cymbals crashing or a high-pitched shaker. While very few musical sounds approach the upper limit of human hearing, there are harmonics — or multiples of the frequency — that surpass it.
Everyone hears a little differently and sounds that are obvious to you may go unheard by others. Interestingly, small children have the best hearing, followed by women, then men.
As we age, our hearing deteriorates naturally. Long exposure to loud or high-impact sounds like a jackhammer will permanently damage hearing, starting with the upper frequencies. As a video editor, it's a good idea to protect your hearing, since sound is 50% of the video equation. This is also a good reason to preview your project's soundtrack with a set of objective ears and on multiple playback systems to help ensure everyone will have a good listening experience.
Grab a Knob (or a Slider)
Equalization is the process of manipulating the frequencies of a recorded sound for a specific effect. It can be done through a mixer as the sound is recorded or in post with EQ plug-ins. One of the simplest forms of EQ is the low-cut filter on various microphones and cameras (see "A Family of Filters" sidebar). This basic EQ switch eliminates wind and handling noise, but can leave the audio a bit on the thin side; use only when needed. Many audio mixers contain simple equalizers that divide the audio spectrum into two, three or four bands. This type of EQ is great for shaping sound as it enters the camera, compensating for different microphones and subjects. But use these equalizers judiciously — there are some things that can't be undone in post.
Equalizers — whether hardware or software — come in two basic flavors: graphic and parametric. Most people are familiar with the ubiquitous row of sliders in a graphic equalizer. Each slider represents a narrow portion of the audio spectrum and can either boost or cut sound in that area. The precision of a graphic equalizer is decided by how many sliders it has. A 10-band EQ splits the audio into one-octave segments for general sound shaping. A 31-band EQ offers separate control in 1/3-octave increments for some serious sonic surgery. Parametric EQs have only a few bands — no more than four or five — but each band can pinpoint a specific frequency or range of frequencies. This makes it easy to make subtle changes to the sound or radical, extensive audio transformations. Today, most corrective EQ is done in software — either in our video editing app or a dedicated audio program. This makes it easy to experiment with alternative settings, recall presets and undo mistakes.
Let's take a typical product video and go through the process from start to finish. First, we have several audio elements. There is dialog from three subjects — one recorded with a shotgun and the other two using lapel microphones. Then, there is the voice-over, supplied by our favorite narrator. Finally, the theme music from our buy-out library. The first step is to do some corrective EQ on the dialog. The shotgun recording has some wind noise, so we'll cut a few low frequencies until it sounds right. The lapel mic dialog sounds stuffy by contrast, so we'll cut a few decibels in the 150-250Hz range. The voice-over and music sound fine as-is and, with a few volume tweaks, the soundtrack is coming together. But now there is a distinct difference between the slick narration and our dialog footage. This is where EQ "sweetening" comes in. By carefully boosting some of the upper frequencies, our vocals start to sparkle. A little low-end boost adds some authority. Maybe a small boost in the upper midrange for clarity and now it sounds great.
EQ is a very subjective process and you should make your corrections carefully. Start by cutting frequencies before boosting everything else. This makes a cleaner sound and won't affect your volume settings. It may take several passes before you are totally happy with the results, but the effort is worth it. Whether carving clean sound from a rough recording or spicing up a finished product, EQ is the perfect audio tool to master.
Contributing Editor Hal Robertson is a digital media producer and technology consultant.
A Family of Filters
Equalization has a first cousin called the filter. Filters allow certain parts of the audio spectrum to pass, while eliminating others. For instance, the High-Pass filter removes all audio below a set frequency, leaving everything else untouched. This is perfect for cleaning up muddy dialog or minimizing rumbling wind noise in your audio. Low-Pass filters work the other way, removing audio above the set frequency — great for getting rid of hiss. Band pass filters have a high and low frequency point, passing only the audio in the middle — a nice way to simulate the sound of telephone or walkie-talkie conversations.