EQ and its effects

Equalisation

Equalisation or EQ for short is the process of altering the frequency response of a sound. The most familiar type of EQ is the treble/bass control.

TREBLE - Adjusts high frequencies

BASS - Adjusts low frequencies

It is used to correct sounds which sound unnatural, eliminate unwanted sounds and make certain sounds more prominent and reduce feedback. There are a few types of equalisation, such as:

BELL EQ - This boosts the range of frequencies focused around a certain point. This point gets effected the most by the EQ whereas the frequencies further from this point are less effected.

PARAMETRIC EQ - This uses bell EQ but have a significant advantage of being able to select which frequency is being adjusted. These equalisers can be found on guitar and PA amps.

SHELVING EQ - This type of equalisation boosts the frequencies within the sound recorded to a certain frequency causing a 'shelf' in the frequency spectrum

GRAPHIC EQ - Depending on the number of sliders you have dictates how much control you'll have over the frequency spectrum of the sound. This way you can manipulate a certain area of the spectrum

Terminology

CUTOFF FREQUENCY The frequency at which a high or low frequency EQ section starts to take effect. Also referred to as turnover frequency.

SLOPE The rate at which a high or low frequency EQ section reduces the level above or below the cutoff frequency. Usually 6, 12, 18 or 24dB/octave.

PASS BAND The frequency range that is allowed through.

STOP BAND The frequency range that is attenuated.

FILTER An EQ section of the following types:

HIGH PASS FILTER A filter section that reduces low frequencies.

LOW PASS FILTER A filter section that reduces high frequencies.

BAND PASS FILTER A filter section that reduces both high and low frequencies.

NOTCH FILTER A filter that cuts out a very narrow range of frequencies.

GAIN The amount of boost or cut applied by the equaliser.

Q How broad or narrow the range of frequencies that is affected.

SWEEP MID A middle frequency EQ section with controls for frequency and gain.

PARAMETRIC EQ An EQ section with controls for frequency, gain and Q.

GRAPHIC EQ An equaliser with a number of slider controls set on octave or third octave frequency centres.

BELL An EQ with a peak in its response.

SHELF A high or low frequency EQ where the response extends from the set or selected frequency to the highest or lowest frequency in the audio range.