Parametric Equalisers

What do parametric equalisers do?

A parametric e.q. is a stand alone/rack unit designed to tackle the most difficult problems in both live and studio situations, some mixers also have this facility at the upper end of the market. Split up into several overlapping frequency bands. Each band has three rotary controls and a bypass switch. The frequency rotary selects the frequency you wish to boost or attenuate your source signal. For the sake of argument lets say it is a four band rack mount unit the first bands selectable frequency would be from 30hz-300hz, the second band would be from 100hz-1khz, the third from 500hz-5khz and the last 2khz-20khz, these frequency bands will vary from manufacturer to manufacturer.

The second rotary will be the amount of cut or boost at the selected frequency by up to + or – 15db. The final rotary is what makes these e.q. so desirable this final knob is marked Q and this determines over how wide or narrow the cut/boost has an effect from two octaves practically the whole of the frequency band exampled in each band down to a 6th of an octave, when the frequency band is so narrow they are often described as notch filters. As mentioned earlier a bypass switch is present per band so you can make a comparison with the original signal. Parametrics are available as solid state and tube devices.

What would I use one for?

Unlike the conventional e.q. found on mixers which have a fixed Q, parametrics offer precise equalisation. You could have a broad bass boost a narrower low mid cut a notch for a particular irritating frequency and a broader boost/cut for the highs. Shaping the e.q. to the room, removing feedback from monitors, getting rid of unwanted overtones in drums, removing string noise on acoustic guitars even removing wrong notes in a recording. Parametrics are a tool you can use for a wide variety of jobs.

Because of the nature of an e.q. a input adjust is there to optimise the signal coming in and an output adjust if a signal has had e.q. cut it may be considerably quieter and need boosting back up, conversely if there has been a lot of e.q. boost then the outgoing signal may need attenuating. - JD