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An Introduction to Equalization - A free download from Audio Masterclass

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Description and application of the equalizer section of the mixing console.

The equalizer has the following sections:

  • High pass filter (cuts low frequencies)
  • Low pass filter (cuts high frequencies)
  • High frequency EQ with controls for frequency and bell/shelf
  • Two mid frequency EQ sections with controls for frequency, gain and Q
  • Low frequency EQ with controls for frequency and bell/shelf
  • EQ in/out switch

In the mid section, there are three parameters that we would like to be able to control. First and foremost is the frequency: this boost could be centred on any frequency according to the instrument and according to which characteristics you want to accentuate. Second is the gain, which is the degree of boost and can be measured in decibels (dB) at the centre frequency. Some mixing consoles have this control calibrated in dB, up to 12 or 15 dB at maximum. Gain can also be negative, producing an EQ cut, which would be written as a gain of -6 dB (or whatever) at the center frequency, so the curve would dip downwards. EQ cut, by the way, is a vastly under used resource on many consoles, but more on this later.

The third parameter is Q. Q is a measure of the 'bandwidth' of the bell-shaped curve. A low Q - 0.3 is low - will allow the EQ to cover a wide range of frequencies, while a higher Q - 5 is high - will allow you to home in on a particular feature of the sound.

The bell-shaped curve is often referred to as 'peaking' EQ, and applies to all mid frequency range EQ sections and a good proportion of high and low frequency EQ sections too. A 'shelving' EQ is where the boost (or cut) extends from the chosen EQ frequency all the way to the extreme end of the range. I have shown a low frequency shelving EQ in boost mode, but it could have been a high frequency cut with a similarly shaped but differently orientated curve. It isn't possible to say which type of curve is better, for it depends on what you want to achieve, but some consoles have a button to allow you to choose.

By David Mellor Tuesday May 20, 2003