What is Equalisation (EQ)?

Equalisation is essentially the cutting or boosting of certain frequencies in the audio spectrum. To be very blunt, they can be described as tone controls.

The name comes from it's original use, which was to correct the problems caused by recording equipment and the recording environment. The idea was to make the recorded sound "equal" to the original sound.

Uses of EQ

Noise Reduction - Rolling off the lows to reduce rumblings, or rolling off the highs to reduce hiss.

Sound Shaping - EQ can enhance a sound by bringing out and emphasising some of it's natural character. Sounds have four component parts (Sub Harmonics, Fundamental Note, Upper Harmonics and High Harmonics). Generally leave the fundamental note alone and boost or cut the others.

Distance Placement - Nearer sounds have more bass and treble. So boost these to bring an instrument to the front, cut these frequencies and boost the mid range to push (thin out)the instrument back into the mix.

Creating room in a mix - Cutting frequencies of certain instruments to make others sit nicer in the mix.

The entire Mix - You need to take into account the mix as a whole. Maybe boost the bass overall to make your body feel the rhythm. Maybe boost the highs to make it sizzle (or give people headaches?)

Types of Equalisers

Fixed EQ

Typically bass, treble or mid. Fixed frequency cutoffs, just the cut or boost is controled.

Filters

Most common are Low and High Pass Filters. Filters are good at getting rid of undesirable sounds at each end of the spectrum. e.g. Hiss reduction.

Filters traditionally only cut frequencies, they do not boost frequencies, however some software EQs allow you to now boost as well

Low Pass - Passes (let's through) frequencies below a cutoff point, attenuates the higher frequencies. The opposite of...

High Pass - Passes the frequncies above the cutoff point and attenuates the lower frequencies.

Band Pass - Passes a band of frequencies and attenuates the frequencies on either side. The opposite of...

Notch - Attenuates a band of frequencies and passes the frequencies on either side.

High Shelf - Boosts frequencies above the cutoff frequency. The opposite of...

Low Shelf - Boosts frequencies below the cutoff frequency.

Shelf Equalisers

As above except they can either cut or boost the signal. There are usually two, one for top (high frequency shelf 8 to 12 kHz) and one for the bottom (Low frequency shelf 80 to 150Hz)

Sweep Equalisers

Allows you to cut or boost selected areas of the sound, often in pairs

Semi Parametric

As per Sweep Equalisers except you can control the width of the frequency affected, by use of a single button.

Fully Parametric

Usually four of these are used together. Three Controls, Frequency, gain and bandwidth. Allows full control of the bandwidth. Normally has a switch on the first and last units for low and high shelf filters. (e.g. EQ section in Cubase).

Graphic Equalisers

Allows the adjustment of a series of bands of fixed frequencies over the entire spectrum.

Paragraphic Equalisers

A hybrid Eq offering several graphic like bands of eq but also has user definable frequency bands like a parametric.

Passive & Valve

Passive equalisers, cut all the frequencies by default. You don't boost frequencies, rather than don't cut them so much. A typical example of this is the tone controls on a guitar. Valve equalisers generally work this way. An amp stage brings the volume to it's original level.

Instrument Frequency Ranges.

These are just some guidelines since all sounds will be slightly different and what is required for each song will be different.. Where is says "add", boost to get the desired effect. Obviously, you probably want to cut frequencies in the muddiness areas. Suggested starting points are in brackets.

Suggestion: One at a time with each EQ knob. Boost it a bit, then sweep the associated frequency, until you find the range that affects the sound the most. Listen to how the sound is shaped by boosting or cutting over that range. Great fun?

General Tips

All EQs sound different, try several different ones and listen to the differences.

It's best to get rid of unwanted noise at source rather than relying on EQ'ing it out later.

Similarly, it is better to get a tonally correct source rather than relying on EQ'ing it later.

EQ can also damage your sound since it also affects timing relationships between frequencies. (a problem with the harshness of early CDs)

Remember it is the sound of the mix that matters, not the sound of an individual instrument.

Changing the EQ on a particular instrument can have an adverse affect on other instruments. e.g. Applying extra bass to guitars \ keyboards can mean loosing the bass or bass drum.

To get rid of the digital sound cut all frequencies above 12kHz

Boosting is normally kept to a few dBs, where as cutting frequencies can be more extreme.

If cutting a frequency doesn't do the trick, repeat it with another cut to the same frequency.

Cutting the midrange of a sound can give the impression that it is louder. Useful for rhythm parts.

Keyboards and Guitars often occupy similar frequency bands. So cut the mid range and boost the bottom and top of one of them and do the reverse for the other.

Use EQ to boost \ cut frequencies within a sound rather than just adjusting the overall volume, which boosts or cuts all frequencies. Useful for multiple guitar parts or for guitars and keys

Changing the EQ of an instrument will affect it's volume. You may need to adjust the volume.

For two parts playing the same thing. Don't necessarily, EQ them apart, since the brain will try to merge them back again. Combine them to make a bigger sound.

No amount of EQ will fix a badly recorded part. It may be better to re-record the part.

If the arrangement is too busy, it may be better to cut parts rather than try to force them in with EQ.

In the muddiness area, don't just cut all the same frequencies from all the instruments. That will leave a hole in the mix. Remove different frequencies from different instruments to fill the audio spectrum.

Low pass the bass and use bell curves on pads, guitars and vocals. Use a high pass on drums (not bass drum (LPF)) to give each instrument room

Rolling off the high frequencies of an instrument will push it further back in the mix (high frequencies are lost over distance).

Beware of boosting guitars in the 1-6kHz range as it will affect the vocals. Boost in the 5-8kHz instead.

When doing close miked recording, due to the proximity, the recording may have an unnaturally high level of bass. You will need to roll this bass off to get the "real sound" back.

Remember EQ is just a tool, you don't need to use it on everything (or if you are lucky anything).

Don't be scared to use extreme EQ. It needs to sound good in context to the other instruments, not necessarily on it's own?

Don't spend too long listening to a sound in isolation.

Double a guitar (or vocal etc) part then EQ them to make them sound different. (opposite of what I've said above).

For telephone type voice. Boost around 1kHz and cut all other by a similar amount.

Live, use EQ to stop feedback. Move the mics towards the speakers to get the feedback, then sweep the frequencies and reduce the volume at the frequency at which the feedback occurs.

Artifical instruments like electric guitars and synths can have a lot of EQ applied to them, to shape them.

As with all effects check the sound with and without the effect to ensure you are not making things worse.

To EQ then Compress or Compress then EQ. Try both, since you will get different effects.

Bear in mind the actual frequency range of the instrument you are Eq'ing. Boosting outside these ranges can add to the noise.

Putting EQ before distortion will allow you to shape the character of the distortion, you can then use the tone controls on the distortion to balance it out. e.g Boosting the bass before the distortion and cutting it after, will give more distortion to the lower guitar strings and less to the top strings.