An Equalizer (usually in a mixer) is a sophisticated tone control, something like the bass and treble controls in a stereo system. Equalization (EQ) lets you improve on reality; add crispness to dull cymbals: add bite to a wimpy electric guitar. Or EQ can make a track sound more natural; for instance by removing tubbiness from a close miked vocal.
To understand how EQ works we need to know the meaning of a spectrum. Each instrument or voice produces a wide range of frequencies called its spectrum...the fundamentals and the harmonics. The spectrum gives each instrument its distinctive tone and quality or timbre.
If you boost or cut certain individual frequencies in an instruments spectrum, you change the tonal quality of that instrument. EQ adjusts the bass, treble, and midrange of a sound by turning up or down certain frequency ranges. That is, it alters the frequency response. For example, a boost (a level increase) in the range centered at 10 kHz makes percussion sound bright and crisp. A cut at the same frequency dulls the sound.
Types of EQ
Equalizers range from simple to complex. the most basic type is a bass and treble control (labeled LF EQ and HD EQ). Typically this type of EQ has up to 15dB of boost or cut at 100Hz (for the low-frequency EQ knob) and at 10 kHz (for the high-frequency EQ knob).
With a 3-band EQ you can boost or cut the lows, mids, and highs at fixed frequencies. Sweep-able EQ is more flexible because you can "tune in" exact frequencies needing an adjustment. If your mixer has sweep-able EQ, one knob sets the center frequency while another sets the amount of boost or cut.
Parametric EQ
Parametric EQ lets you set the frequency, amount of boost or cut, and bandwidth...the range of frequencies affected.
Graphical EQ
A graphic equalizer is usually outside the mixing console. This type has a row of slide pots that work on 5 to 31 frequency bands, When the controls are adjusted, their positions graphically show the resulting frequency response. Usually, a graphic equalizer is used for monitor-speaker EQ, or is patched into a channel (Waves EQ plug-ins) for sophisticated tonal tweaking...
Equalizers can also be classified by the shape of their frequency response. Peaking EQ shapes the response like a hill or peak when set for a boost. With shelving EQ, the shape of the frequency response resembles a shelf. A filter causes roll-off at the frequency extremes. It sharply rejects (attenuates) frequencies above or below a certain frequency. There are generally 3 types of roll-off filters; lowpass, highpass, and bandpass.
For example, a 10 kHz lowpass filter (high-cut filter) removes frequencies above 10 kHz. Its response is down 3dB at 10 kHz and more above that. This reduces hiss-type noise without affecting tone quality a much as a gradual treble roll-off would. A 100 Hz highpass filter (low-cut filter) attenuates frequencies below 100Hz. Its response is down 3 dB at 100 Hz and more below that. This removes low-pitched noises and rumble such as air-conditioners, furnaces, fans, cars driving by, or breath pops. A 1kHz bandpass filter cuts frequencies above and below a frequency band centered at 1 kHz.
The crossover filter in most monitor speakers consists of lowpass, highpass, and bandpass filters. They send the lows to the woofer, mids to the midrange, and highs to the tweeter. A filter is named for the steepness of its roll-off: 6dB/octave (first order), 12 dB/octave (second-order), 18 dB/octave (third-order) and so on...
_____________________________________________________________________________________
.