How To Use EQ
If your mixer has bass and treble controls, their frequencies are preset at the factory (usually at 100 Hz and 10 kHz).
Set the EQ knob at 0 to have no effect (“flat” setting). Turn it clockwise for a boost; turn it counter-clockwise for a cut. If your mixer has sweepable EQ, one knob sets the frequency range while another sets the amount of boost or cut.
As we said, the tone quality of a voice or instrument depends on the relative levels of its fundamentals and harmonics. Listed below are the fundamental and harmonic frequencies for female and male voices:
Female voice fundamentals: 175 Hz -1.175 kHz
Female voice harmonics: 2 Hz-12 kHz
Male voice fundamentals: 87 Hz-494 Hz
Male voice harmonics: 1 Hz-12 kHz
Basically, if the sound is thin or lacking fullness, turn up the lower end of the fundamentals. If the tone is too bassy or tubby, turn down the fundamentals. If it’s muddy or unclear, turn up the harmonics. Turn down the harmonics if the tone is too harsh or sizzly.
Below is a list of common sound problems and suggested EQ settings that can fix them. The amount of boost or cut is up to you – whatever sounds right. About 3 to 6 dB should be all you need in most cases.
Puffy, nasal, or chesty: Cut 500 Hz to 800 Hz
Dull, muffled, sibilants are hard to hear: Boost 10 kHz
Sizzly, “s” sounds are too strong: Cut 10 kHz
Bassy, boomy: Cut 100 Hz (males) or 200 Hz (females)
Thin, tinny: Boost 100 Hz (males) or 200 Hz (females)
Uses Of Equalization
Here are some applications where EQ comes in handy.
Improving tone quality: This is the main use of EQ, as described above.
Special production effects: Extreme equalization reduces fidelity, but it also can make interesting sound effects. Sharply rolling off the lows and highs on a voice, for instance, gives it a “telephone” sound. A 1 kHz band-pass filter does the same thing.
Reducing noise: You can reduce unwanted low-frequency sounds—air-conditioner rumble, floor thumps, and breath pops—by turning down low frequencies below the voice range. For example, a female actor’s lowest frequency is about 200 Hz, so you’d set the equalizer’s frequency range to 40 or 60 Hz and apply cut. This roll-off won’t change the actor’s tone quality, because the roll-off is below the actor’s voice range. Better yet, use a high-pass filter (low-cut filter) set to 200 Hz.
Compensating for microphone placement: Often you must place a lavalier microphone under a costume in order to hide the mic. Unfortunately, the costume fabric does not transmit the mouth’s high frequencies well, so you hear a dull, muffled tone quality.
A high-frequency boost on the console can compensate for this loss. (Just be careful not to cause feedback). Placing a lavalier mic on the chest creates a rise in the response around 730 Hz, which can give a chesty or puffy quality. Applying an EQ cut at the same frequency will result in a more natural sound.
Headworn mics may or may not need EQ, depending on the microphones’ frequency response. The voice sounds brightest when miked in front, and becomes progressively duller to the side, above, or below the mouth.
The proper use of EQ is basically simple. Know the sound of the unamplified human voice, and adjust the EQ knobs to make your PA sound like that.
A member of AES and SynAudCon, Bruce Bartlett is a live sound and recording engineer, microphone designer (http://www.bartlettaudio.com), and audio journalist. His latest book is Practical Recording Techniques, 6th Edition.