Fixed band EQ

Fixed band EQ, also known as fixed EQ or 3 band EQ, is the most simple type of EQ. It's commonly found on guitar amps, some bass amps, keyboard amps, budget mixing desks and audio amplifiers. Fixed EQ will have one knob for each frequency, most commonly bass, mid and treble. Fixed EQ is exactly what it says, a boost or cut gain control at a fixed frequency. They also have a fixed Q, which is generally wide so it effects the sound more. For example the frequency of a fixed EQ bass knob might be 50Hz and the knob will increase or decrease the gain at that frequency. Early EQ's were fixed band which is why a lot of old 60's records sound full, due to the wide Q.

Semi parametric

Semi parametric, also know as sweepable mid EQ or mid sweep, is possibly the most common type of EQ. It's found on a lot of semi professional mixing desks, hardware EQ's and channel strips. Semi parametric is a mix between fixed EQ and parametric. It usually has 3 bands, low mid and high but you can change the frequency of the mid band, hence the "sweepable mid EQ" nickname. The rest of the EQ works the same as a fixed band EQ. The idea behind just having the mid frequency band sweepable is that this is the most densely populated frequency band which causes a muddy or full sound, therefore it should need more accuracy and control. It's worth noting that some semi parametric's will have a selectable frequency for low mid's and high maids, which is basically splitting the mid frequency into two bands for more accuracy.

Fully parametric

Fully parametric is the most advanced, accurate and controllable EQ. Fully parametric EQ is usually found on dedicated hardware EQ's and many software plugin EQ's, very rarely you'll find it on a professional mixing desk. Parametric EQ means that every band has a separate frequency, Q and gain control which means that every frequency can be boosted or cut. The amount of bands vary's with some software plugins having ten bands but the average is 7 bands. Parametric EQ is used for total control of the frequency's of a signal. This means you can do some serious EQ fix's, for example there's a high pitched noise at exactly 12K, well just dial 12K, change the Q to ultra narrow then decrease the gain until it's no longer audible. The small Q will mean only a narrow section of the frequency band will be effected, therefore minimize the loss of other frequency's.

Graphic EQ

Graphic equalisers work totally different to parametric and fixed EQ but also incorporate some of the designs. The way they work is to have a set of sliders, usually 20 to 30, each with its own fixed frequency band. The sliders control the gain of each frequency. Graphic EQ's are useful because they allow the user to quickly change the gain of frequency's by just moving the slider. They are most commonly found patched over a master output to EQ the whole mix.. They are most commonly found in live sound rig and some studios which have acoustic problems.

Conclusion

So now you know all about the different types of EQ. Usually a semi parametric or fully parametric EQ will be the type you use the most, mainly because of their flexibility. Even if you don't use all the bands on say a 10 band EQ you always have the option to use them if needed. I will be posting a how to use EQ tutorial soon. I hope you found this tutorial useful. Hopefully it will help you purchase the right EQ for your needs.

Zander

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