Equalizers

Equalization An equalizer can be defined as a frequency

selective amplifier. It is a device that can alter the spectral

content of a signal that passes though it. It is used to compensate for variations or

discrepancies in frequencies present in audio signal.

Equalizer allows the engineer to accentuate or attenuate (cut or boost in simplified terms) any frequency or group of frequencies within the audio spectrum.

Frequency Response It displays the amount of energy (amplitude) at any given

frequency compared to unity gain. The vertical (Y) axis of the plot displays the amplitude information, while the horizontal (X) axis displays the frequency bandwidth being measured.

The straight horizontal line (usually labelled zero) shows the amplitude level of the incoming signal – unaffected by the EQ. It represents unity gain.

Bandwidth The definition of bandwidth is the distance (or the

frequency bandwidth) between the 3dB down points. Bandwidth is measured in octaves.

Bandwidth is measured in octaves. Some EQs have Q control instead of bandwidth control.

This accomplishes the same thing, but is measured differently. Q is determined by dividing the centre frequency by the difference between the upper 3dB down point and the lower 3dB down point

Equalizer Types Parametric Equalizers Bell Curve (Peaking EQ) Shelving EQ Graphic Equalizer

Parametric Equalizers A parametric EQ is named for the user’s ability

to adjust all of the parameters of equalization. The parametric EQ allows manipulation of amplitude centre frequency, and bandwidth.

Parametric Equalizers In true parametric EQ, all four bands will have

continuously variable amplitude (cut/boost) frequency, and bandwidth controls.

Amplitude (Cut/Boost) : The amplitude controls provide a certain amount of cut or boost at the selected frequency range, usually affecting the centre frequency by ±12dB to ±18dB.

Frequency : The frequency control allows the engineer to tune in to a particular centre frequency. Each band provides a sweepable range that overlaps its neighboring bands.

Bandwidth : The bandwidth control determines what frequencies below and above the centre frequency will also be affected by the cutting or boosting process.

Bell Curve (Peaking EQ) The bell curve characteristic (or peaking

characteristic) has the most affect on the center frequency/. The information above or below the center frequency (sidebands) is affected according to the width of the bell.

Shelving EQ A shelving EQ will treat all frequencies equally – an

even amount of boost or cut for all frequencies beyond or before its knee frequency (cut-off frequency).

In a low frequency shelving EQ, all information below the selected frequency is affected equally. In a high frequency shelving EQ, all the information above the selected frequency is affected equally.

Graphic Equalizer The graphic equalizer derives its name from its

front panel layout, which reflects its functions graphically by dividing the audio spectrum in to a number of separate frequency bands which can be modified independently.

Equalizer Types

Understanding EQ and its Effects on Signals Vocals

The speech spectrum may be divided into three main frequency bands corresponding to the speech components known as fundamentals (formants), vowels, and consonants.

Speech fundamentals occur over a fairly limited range between about 125Hz and 250Hz. The fundamental region is important in that it allows us to tell who is speaking, and its clear transmission is therefore essential as far as voice quality is concerned.

Vowels essentially contain the maximum energy and power of the voice, occurring over the range of 350Hz to 2000Hz. Consonants occurring over the range of 1500Hz to 4000Hz contain little energy but are essential to intelligibility.

80Hz to 125Hz Sense of power in some outstanding bass singers.

160Hz to 250Hz Voice fundamentals 315Hz to 500Hz Important to voice quality 630Hz to 1kHz Important for a natural sound.

Too much boost in the range produces a honky, telephone-like quality.

1.25kHz to 4kHz Accentuation of vocals 5kHz to 8kHz Important to vocal intelligibility. 5kHz to16kHz Too much in this area can

cause sibilance.

Filters A filter is a circuit that sharply reduces the

amplitude of signals of frequency outside of specified limits.

The unaffected region is called the PASSBAND, and the filter type is named after the passband as low-pass, high-pass, or band-pass.

Types Of Filters

Hi Pass [Low Cut] Low Pass [Hi Cut] Band Pass Notch

Hi Pass [Low Cut] Attenuates frequencies below the cut off

frequency. Suitable for rolling off low frequency rumble in the signal source.

Low Pass [Hi Cut] Attenuates frequencies above the cut off frequency.

Suitable for rolling off higher frequency content of the signal which is unwanted (i.e. hi frequency rings, etc.)

Band Pass Attenuates frequencies below andabove the cut off

frequencies to create a bandwidth limiting filter This design can be achieved by combining a hi-pass and a lo pass filter.

Notch A very high Q attenuating filter which attenuates

a narrow range of frequencies for a specific frequency centre. Examples of its use is to remove obtrusiveelectrical hums and groundloops.