Equalisation, or EQ for short, is the process of adjusting the balance of different frequency components in an audio signal. EQ can be used to enhance or reduce certain aspects of the sound, such as brightness, warmth, clarity, or depth. EQ can also be used to correct problems in the recording, such as noise, hum, or feedback.

EQ is one of the most essential tools for audio production, as it can make a huge difference in how the sound is perceived by the listener. EQ can help to create contrast and interest in the mix, by making each sound source stand out from the others. EQ can also help to create a sense of space and dimension in the sound, by simulating the effects of distance and acoustics. EQ can also help to achieve a consistent and balanced sound across different devices and platforms, by matching the frequency response of the output system.

There are different types of EQ that can be used for different purposes and effects. Some of the most common types are:

• Graphic EQ: This type of EQ allows the user to adjust the level of a fixed number of frequency bands, usually ranging from 10 to 31. Graphic EQ is often used for live sound applications, as it can quickly and easily correct feedback issues or match the sound system to the venue.
• Parametric EQ: This type of EQ allows the user to adjust the level, frequency, and bandwidth (or Q) of a variable number of frequency bands, usually ranging from 1 to 8. Parametric EQ is often used for studio production applications, as it can precisely and flexibly shape the sound of individual tracks or groups.
• Shelving EQ: This type of EQ allows the user to adjust the level of all frequencies above or below a certain cutoff frequency. Shelving EQ is often used for mastering applications, as it can subtly enhance or reduce the overall brightness or warmth of the mix.
• Filter EQ: This type of EQ allows the user to remove all frequencies above or below a certain cutoff frequency. Filter EQ is often used for creative or corrective applications, as it can create dramatic effects or eliminate unwanted noise.

EQ is a powerful and versatile tool that can improve any audio production. However, it is important to use it with care and moderation, as too much or too little EQ can ruin the natural sound quality and dynamics of the audio. A good rule of thumb is to use EQ to cut rather than boost frequencies, as this can reduce unwanted side effects such as distortion or phase issues. It is also advisable to use a reference track or a spectrum analyzer to check the frequency balance and avoid over-EQing.

Using EQ effectively in audio production requires some knowledge and practice of the basic principles and techniques of EQ. Here are some tips and guidelines to help you use EQ more efficiently and creatively:

• Know your frequency spectrum: The frequency spectrum is the range of audible frequencies, from 20 Hz to 20 kHz. Different frequency ranges have different characteristics and effects on the sound. For example, low frequencies (below 250 Hz) provide the bass and sub-bass elements of the sound, such as kick drums, bass guitars, or synthesizers. Mid frequencies (between 250 Hz and 4 kHz) provide the body and presence of the sound, such as vocals, guitars, pianos, or horns. High frequencies (above 4 kHz) provide the brightness and detail of the sound, such as cymbals, hi-hats, or strings. Knowing the frequency spectrum can help you identify and adjust the elements of the sound that need EQ.
• Use your ears: The most important tool for using EQ is your ears. You should always listen to the sound before and after applying EQ, and compare it to the rest of the mix. You should also listen to the sound in different contexts, such as soloed or in a group, or on different speakers or headphones. You should also listen to the sound at different volume levels, as loudness can affect how you perceive the frequency balance. The goal of using EQ is to make the sound better and more pleasing to your ears, not to follow any rules or presets.
• Use subtractive EQ: Subtractive EQ is the technique of cutting or reducing frequencies that are unwanted or problematic in the sound. Subtractive EQ can help to clean up and clarify the sound, by removing noise, hum, rumble, hiss, or feedback. Subtractive EQ can also help to create space and separation in the mix, by removing overlapping or competing frequencies between different sound sources. Subtractive EQ can also help to enhance or emphasize certain frequencies in the sound, by creating contrast and focus. Subtractive EQ is usually preferred over additive EQ, as it can achieve better results with less side effects.
• Use additive EQ: Additive EQ is the technique of boosting or increasing frequencies that are desired or beneficial in the sound. Additive EQ can help to enrich and improve the sound, by adding brightness, warmth, depth, or color. Additive EQ can also help to create interest and excitement in the mix, by adding harmonics, distortion, or modulation. Additive EQ can also help to correct or compensate certain frequencies in the sound, by matching or balancing them with other sounds or systems. Additive EQ should be used with caution and moderation, as it can introduce unwanted side effects such as distortion, phase issues, or masking.
• Use a high-pass filter: A high-pass filter is a type of filter EQ that removes all frequencies below a certain cutoff frequency. A high-pass filter can help to clean up and tighten the low end of the mix, by removing unnecessary or excessive bass frequencies that can muddy or clutter the sound. A high-pass filter can also help to prevent low-frequency interference or feedback from microphones or speakers. A high-pass filter should be applied to most sounds in the mix, except for those that need to provide bass or sub-bass elements.
• Use a low-pass filter: A low-pass filter is a type of filter EQ that removes all frequencies above a certain cutoff frequency. A low-pass filter can help to smooth out and darken the high end of the mix, by removing harsh or brittle frequencies that can fatigue or irritate the ears. A low-pass filter can also help to create a sense of distance or atmosphere in the sound, by simulating the effects of air absorption or reverb. A low-pass filter should be applied sparingly and selectively in the mix, only to those sounds that need to be pushed back or softened.