EQ is the second most important tool available to the mix engineer. It is a powerful tool for changing the tone of a sound.
As a basic example, think about the tone controls on a home music player (such as CD player or computer speakers). There might be two controls – ‘treble’ and ‘bass’. The treble control adjusts the high frequencies – turning it up makes the sound brighter, and sometimes sharper or harsher. Turning it down makes it duller, and sometimes indistinct. The bass control adjusts the low frequencies – turning it up makes the sound heavier and thicker, and sometimes woolly or muddy. Turning it down makes the sound lighter, and sometimes weaker and thinner.
The EQ available to a mix engineer usually has these basic treble and bass controls (often called ‘high shelf’ and low shelf’). Mix EQ often also has much more sophisticated capabilities. There are usually one or more midrange EQ controls as well as ‘high cut’ and ‘low cut’ filters (which are like extreme versions of the shelf controls).
Mix EQ controls are usually organised into ‘bands’. One band has a single effect on the sound, but may have several controls to adjust how that happens. The most common band controls are:
- Gain – This is the most audible control, and adjusts how strongly
- the band affects the sound. Positive gain adds energy to the sound, making it louder. Negative gain reduces energy from the sound, making it quieter. The further away from 0dB (either positive or negative) this controls is, the more audible the effect is.
- Frequency – This affects where the band affects the sound. Higher values affect higher frequencies, lower values affect lower frequencies. To best experience this, set the gain of a band to something reasonably high (such as +12dB) and listen to how different frequency settings sound. Similarly, try setting the gain to something negative (such as -12dB) and listen.
- Q – This is the most subtle control. It’s sometimes referred to as ‘width’. Some EQs don’t even have this control. Q determines how ‘focussed’ the band is (the EQ band, not the musicians!). Higher values cause the band to get narrower, meaning the tonal change gets sharper and more surgical. Lower values cause the band to get wider, meaning the tonal change is broader. When this control is labelled ‘width’ instead of ‘Q’, the values are usually reversed – higher values make the band wider, lower values make it sharper.
Your approach to using EQ in a mix will depend entirely on the raw sound of the recorded tracks and how you want to shape them to work together with the other tracks. As a general starting point, though, think back to the basic music player tone controls:
- If you want the sound brighter, turn up the higher frequencies. • If you want the sound duller, turn down the higher frequencies. • If you want the sound heavier, turn up the lower frequencies.
- If you want the sound lighter, turn down the lower frequencies.
- If you want the sound more present, turn up the middle frequencies.
- If you want the sound smoother, turn down the middle frequencies.
- You’ll often – but not always – get better results by turning down (negative gain), rather than up (positive gain)