EqualizationEqualization

Changing the curveChanging the curve

What is an EQ?What is an EQ?

• An Equalizer – Is generally a frequency-specific amplifier– Is made up of filters (passive or active)– Is one of the most powerful tools an engineer

has

A bit more about frequencyA bit more about frequency

• Most sounds are made up of a spectrum of frequencies (i.e. not one single frequency)

• The lowest frequency in the spectrum is called the fundamental. This is usually the perceived pitch

• Other frequencies are called overtones. These can be classified as harmonics or partials

• Joe Fourier: “any complex periodic wave can be synthesized from sine waves of different frequencies, amplitudes, and time relationships”

• Source: Master Handbook of Acoustics; F.Alton Everest

Example FFTExample FFT

Insert Sound File Here

Frequency “Bands”Frequency “Bands”

• “Band” refers to a group or range of frequencies– The FM broadcast band ranges from 87.5

MHz to 108.0 MHz

• “Bandwidth” defines the size of the range– the bandwidth of human hearing is

approximately 20 kHz

What we hearWhat we hear

20 Hz 100 Hz 200 Hz 1 kHz 3 kHz 8 kHz 10 kHz 20 kHz500 Hz

Fundamentals of most

instruments

Presence, sharpness Clarity ->Air

“sizzle” crispness

Impact, rumble,

deep bass, “size”

Low Frequencies Low “Mids” High “Mids” High Frequencies

Basic Filter ConceptsBasic Filter Concepts• A basic filter generally does not amplify• Attenuate – “to weaken” – Webster’s II New Riverside Dictionary

• Pass band – range of frequencies the filter will not attenuate• Stop band – range of frequencies that will be attenuated by the filter• Corner or Cutoff frequency – essentially the border between the pass band

and stop band. Attenuation is -3dB at this frequency

• Are measured by “nth order” where n represents 6 dB per octave attenuation– 1st order = -6dB per octave slope– 2nd order = -12dB per octave slope

• Types of filters– High pass (low cut)– Low pass– Band pass– Notch

• Active Filters can amplify or attenuate

Shelving FiltersShelving Filters

• A shelving filter can boost or cut– A low shelf will boost or cut all frequencies below the

cutoff frequency– A high shelf will boost or cut all frequencies above the

cutoff frequency• Bass and Treble controls on most consumer stereo

equipment are shelving filters

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““Peak-and-dip” filterPeak-and-dip” filter

• Amplifies or attenuates a band centered on a particular frequency

• Q – the bandwidth of the frequencies being effected– Higher Q value means narrower band

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Types of EqualizerTypes of Equalizer

• A number of “peak-and-dip” filters with fixed Q and center frequency

• Generally used in live sound situations to “tune” the room and control feedback

• Commonly have up to 30 filters (bands) with a 1/3-octave bandwidth

Graphic EQGraphic EQ

Parametric EQParametric EQ

• Allows you to control the frequency and bandwidth (Q) of the filter

• Most powerful type of EQ for tone shaping• Usually only a few bands