Using a graphic and parametric equalizer

Using a graphic equalizer
Graphic equalizers divide the frequency spectrum into a specific number of bands and assign a fader to each band, as shown in Figure 1. The number of bands varies, depending on the hardware or software. The more bands you have, the narrower the range of frequencies you're affecting when you move a fader up or down.


Figure 1: A typical graphic equalizer (Sony Sound Forge)

Using a graphic equalizer couldn't be easier; you just grab a fader and push it up or down. If you're not sure exactly which frequency you want to work on, don't be afraid to experiment. Grab a fader, push it up, and preview the result. You should be able to hear that frequency being boosted in your file. If you can't hear it, push the fader up even more. Push it up until the frequency is horribly exaggerated. Don't worry; this is how audio engineers do it. Exaggerate to find the frequency, and then scale back the EQ until you've achieved the effect you're after.

This also works when you're looking for a frequency that you want to get rid of. If you can hear a nasty frequency, for example a noisy hiss or even a honking quality to a vocal, hunt for the frequency by boosting until you find the frequency that you're after. Sure, it will make your file sound even worse, but after you find the offensive frequency, you can cut it knowing you're cutting in the right place.

Remember that you want to boost wide and cut narrow. If you're boosting a particular frequency, you should also boost the frequencies on either side — about half the amount you're boosting the target frequency, so you get a nice EQ curve. If you're cutting, cut only the offensive frequency. Don't cut too much; it will make your audio sound hollow and unnatural. If you've ever seen an audio engineer use a graphic EQ, you'll see them adjust their settings to get a nice smooth looking curve, perhaps with one or two nasty frequencies cut.

Using a parametric equalizer
Parametric EQ is slightly different from graphic EQ, because you don't have faders for specific frequencies. Instead, you choose a frequency, how much around your target frequency you want to affect and how much you want to boost or cut. Parametric EQ is usually implemented using knobs, with a separate knob for the frequency, the Q (which is the term used for the width of the effect), and the amount of boost or cut. Some parametric EQ systems don't provide control of the Q; this is known as semi-parametric EQ.

Some parametric EQ also have a little switch that changes the EQ from standard parametric to shelving EQ. Shelving EQ affects all frequencies above or below the frequency setting. Shelving EQ that affects all frequencies below the target frequency is known as high pass, because all frequencies above the target frequency are passed through untouched. Similarly, shelving EQ that affects frequencies about the target frequency is called a low pass shelf, because all the low frequencies are passed.

Tip The EQ knobs on cheaper mixing desks are often fixed-frequency. They're also often shelving, so they're really not precision instruments. If you're going to use the EQ on your mixing desk, use it sparingly. After you've recorded EQ to "tape," it's hard to remove.


Figure 2 shows a software parametric EQ. You can see that it offers four fully parametric controls, along with both high and low pass EQ. Using a parametric EQ is very much like a graphic EQ, with the added ability to adjust the Q. To find the frequency you want, choose a very narrow Q and boost that frequency. Preview your audio, and move the frequency setting back and forth until you hit your target. Next, set your Q (remember: boost wide, cut narrow). Then adjust the boost or cut until your audio sounds the way you want it. If you want to work on another frequency, just use the same approach: Find, set your Q, and apply the right amount of boost or cut.


Figure 2: A software parametric equalizer (Sony Sound Forge)