(cont)
A Parametric EQ, however, has controls for varying the Q and varying the centre frequency of its filters. It is therefore a more precise tool but tends to be complicated to set up, and because of this is best left to an experienced sound operator. The BSS Varicurve uses Parametric EQs.

The EQ section of mixing consoles tend to have sweep-type EQs, where there are a few filters (commonly four), but some (usually the Mids) or all have variable centre frequencies. A high end console may also have a two position Q switch, giving a choice of high or low values.

All these EQs can be used for artistic effect, to 'sweeten' a vocal sound or make it cut through the mix, or to add 'punch' to a drum sound. Sometimes, the unit may be used to effect the overall tonal balance of a mix.

They may also be used to try and correct room resonances and therefore reduce the possibility of feedback at certain resonant frequencies.
Be aware that injudicious use of equalisers, particularly boost, can reduce the headroom of a system, and even send signals into distortion. If you apply EQ boost, you must always check that you do not also need to reduce the gain of a signal.