EQ comes into play when faders are not fulfilling our mix needs. EQ is an acronym for the term Equalisation - to make equal.
In this lesson, you will learn the fundamentals of equalisation and how to use an equaliser in your productions and audio mixes.
What is EQ or Equalisation in Music?
Equalisation is a term that is taken from the corporate world and means— "to make equal; Or to compensate for; Or to make uniform, especially to distribute evenly or uniformly among people.”
In music, equalisation (or EQ in short) means – to even out, reduce or boost sound frequencies. Here we are working with sound frequencies and their levels. EQ-ing can be thought of as a process of selective levelling. You work with a specific set of sound frequencies and their levels.
Equalisers are used to EQ sound. An equaliser adjusts the levels of different frequency regions relative to each other. An equaliser can be a hardware or software-based sound processor.
To understand Equalisation, understanding frequency, frequency spectrum, and amplitude is a must. You must think in terms of sound and frequencies.
The frequency of sound is the number of repetitions of a sound wave per second. Frequency is measured in Hertz (Hz). The higher the repetitions, the higher the frequency. Human ears can hear sound waves that have a frequency between 20 HZ and 20 kHz.
Amplitude on the other hand is the measure of loudness. It is measured in decibels (dB). A change of 6dB leads to doubling/halving of power of sound, and a change of 10dB leads to doubling/halving of perceived volume by the listener. So it is always advised to work in steps like 1.5 dB, 3 dB, 6 dB, 9 dB and so on,
If you wish to learn more about the fundamentals and characteristics of sound, check out the below article
Sound Frequency Spectrum
Lower frequencies are more bass-rich(20Hz-150Hz). As the frequency increases, the pitch increases, and the sound turns towards the Mids(250Hz-2.5kHz and Treble(5kHz and above).
Understanding of frequency spectrum is critical to EQ like Pros.
Below is a table depicting how frequencies are distributed for the human hearing range.
Frequency Range Sound Characteristic
20Hz—40Hz Sub Bass
150Hz—250Hz Upper Bass
250 Hz—2.5kHz Mids
2.5kHz-5kHz Upper Mids
So before EQ-ing, always analyse a sound and have a reason to EQ. Think in terms of sound frequencies. Whether your sound requires EQ-ing in Low-End, Mids or Highs. You should always have a reason to use an Equaliser.
When To Use an EQ
Before you EQ, you should always have a reason as to why you need an EQ. Most beginners tend to overuse Equalisers.
Here are a few reasons when you should consider using an EQ: -
- There are times when during a mix or sound design, you feel like the sound's different frequency regions require different fader levels. This is one clear sign that you require an EQ on the sound.
- When different sounds are getting masked. i.e., one sound is dominating the other. EQ can be used to create space for individual sounds and make them audible in the mix.
- To add clarity and tightness to sounds or a mix. Subtractive EQ-ing is widely used to make sounds clear and punchy.
- To Boost certain frequency regions and make them more prominent or audible.
- To change sound characteristics. EQs can be used to completely alter and change sounds. This is not a common use but still one that cannot be ignored.
Equalisers are used to EQ sound. An Equaliser adjusts the levels of different frequency regions relative to each other. With an EQ you can cut, boost or alter certain sound frequencies using filters. An equaliser can be a hardware or a software-based sound processor.
It is important to understand Equalisers, their types and how they work to understand the equalisation process and its applications. So let us understand different types of EQs.
Types Of EQ
There are three main types of EQ used in audio: -
- A graphic EQ is made up of a bank of different slider controls that are used to increase or cut specific frequency ranges. The bands and frequency ranges are preset for each slider. You can adjust the amplitude using the sliders. The range of amplitude adjustment can be somewhere from ±6db to ±15db, which depends from manufacturer to manufacturer.
- Graphic EQs have the least flexibility in terms of sound manipulation, and hence are easy to use. Graphic EQ can consist of 3 sliders or more. E.g. A standard five-band graphic equaliser comprises sliders for the following fixed frequencies: 30 Hz (low bass), 100 Hz (mid-bass), 1 kHz (midrange), and 10 kHz (upper midrange), and 20 kHz (treble or high-frequency).
- A parametric Equaliser provides a user with more flexibility. Users can control and alter all parameters according to taste and needs, hence the name parametric EQ. You may alter/control three aspects of a parametric equaliser: the level (raising or cutting decibels), the specific frequency, and the bandwidth or range (also known as Q or quotient of change) of each frequency.
- Each frequency, like the graphic equaliser, can be lowered or enhanced. However, unlike graphic equalisers, parametric equalisers let you select a centre or principal frequency and alter it according to your needs, providing a lot more flexibility. For example, if a graphic equaliser has a fixed control at 50 Hz, a parametric equaliser can be adjusted to control frequencies at 40 Hz, 45 Hz, 50 Hz, 55 Hz, 60 Hz, and so forth. With a parametric EQ, one can dig deep into complex equalisation tasks.
Semi Parametric EQ
- A semi-parametric EQ as the name suggest provides a user with complete freedom for not all but certain parameters. In a semi-parametric EQ, a user can alter/control parameters like frequency and amplitude but not Q value, i.e., bands. Frequency Bands are generally predefined. Some semi-parametric EQs provide users with options to alter Q values as well but to some extent. In semi-parametric EQ the gain range is also limited to ±15-18db, while in parametric EQ one can alter gain up to +-60db with ease.
- So in a nutshell, with a semi-parametric EQ one can make alterations but with certain limitations. These limitations make semi-parametric EQ one of the best tools, as they provide speed and ease of use while mixing.
EQ Filter Types
Understanding the various filter types and how they affect the signal is also critical. To cut, boost or alter frequencies, filters are used. Filters of an EQ help you select and alter frequencies as per your sound or mix need. Below are the primary EQ filter types:
Low Cut / High Pass Filter
A low-cut filter filters out all frequencies below a certain frequency cut-off point. For, e.g., if you set a low-cut filter at 100Hz, all frequencies below 100Hz will be cut out or removed.
An important parameter to understand while using a low-cut filter is the slope. The slope determines how aggressively or gently the frequencies will be rolled off for a low-cut filter.
A slope of 6db will gently roll off the frequencies below 100Hz in the above example, and a Slope of 48dB will aggressively cut out the frequencies below 100Hz in the above example.
To remove undesired low frequencies, use a low-cut filter.
Because a low cut filter passes all high frequencies above the cut-off point, this filter is also called a high pass filter.
Low Shelf Filter
A low-shelf filter reduces or increases frequencies below a certain frequency point. Low shelf filters, unlike low cut filters, do not completely eliminate frequencies. Rather, they gradually reduce or increase bass frequencies.
Use a shelf filter to amplify or diminish low-frequency frequencies without totally cutting them off. It is effective for making large tone shifts without losing all the information.
For, e.g., if you set a low shelf filter at 100Hz, all frequencies below 100Hz will be lowered or boosted accordingly by a user-defined value.
High Cut / Low Pass Filter
A high-cut filter is the opposite of a low-cut filter. A high cut filter eliminates/ cuts off all frequencies above a certain frequency cut-off threshold. Because it passes all low frequencies below the cut-off point, this filter is also known as a low pass filter.
To remove undesired high frequencies, use a high-cut filter.
For, e.g., if you set a high-cut filter at 100Hz, all frequencies above 100Hz will be cut out. If you set a high-cut filter at 10kHz, all frequencies above 10kHz will be cut out. How aggressively the cut is made depends again on the slope value.
High Shelf Filter
A high shelf filter lowers or enhances sounds over a certain frequency point. High shelf filters, unlike high cut filters, do not totally shut out frequencies. Instead, they gradually reduce or increase treble frequencies. These are the opposite of a low-shelf filter.
Use a shelf filter to amplify or diminish high-end frequencies without totally cutting them off.
For, e.g., if you set a high shelf filter at 100Hz, all frequencies above 100Hz will be lowered or boosted accordingly by a user-defined value. If you set a high shelf filter at 10kHz, all frequencies above 10kHz will be lowered or boosted accordingly.
Bell Curve Filter
A bell curve lessens or enhances frequencies in the vicinity of a specific centre frequency point. The breadth or bandwidth of the bell curve is determined by the Q value. Higher Q values make a narrow band and lower Q values make a wide range band.
Bell curves are used to precisely amplify or lower a band of frequencies. Peak filters are another name for bell curve filters.
For example, you can use large curves at 100Hz to augment lower frequency zones or you can also make a narrow 100Hz bell to cut or subtract precise regions.
A notch filter reduces the frequency range surrounding a particular centre frequency point. On either side of the frequency range, low and high frequencies get passed and only the notch region is removed. Band stop filters are another name for notch filters.
A notch filter can also be made using a bell curve filter with extreme gain and Q values.
Notch filters are also useful as a subtractive EQ tool. To cut a variety of frequencies, use a notch filter. Tonal shaping effects can also be achieved by modulating notch filters.
A band pass filter passes a frequency range around a fixed centre frequency. Outside of the range, low and high frequencies are muted. To isolate a range of frequencies, use a band pass filter.
Multiband equalisers divide the audio spectrum into pieces using several band pass filters. A band pass can also be created by combining a low cut and a high cut filter.
For example, you can use a low cut filter at 500 Hz and a high cut at 1500Hz to create a band pass filter.
EQ is a powerful tool. it can completely change the way anything sounds. Most mix engineers spend a lot of time EQing. How you use an EQ is of critical importance. It can be used to boost and cut frequencies.
There are four-five EQing Techniques:
- Subtractive EQ: In subtractive EQ you cut out the frequencies that are not required or are troublesome. Cutting out or lowering the amplitude of problem frequencies in a mix by utilising an equalizer plugin is more often the first and common approach to EQing a mix. Always cut before you add or boost frequencies. This adds clarity, makes space and adds tightness to a mix.
- Additive EQ: In additive EQ, frequencies are boosted. Boosting the amplitude of frequencies helps achieve the desired tone and makes any certain sound stand out in a mix. Additive EQ is done mostly after subtractive EQ while mixing.
- Mid-Side EQ - Mid-Side (M/S) EQ is a type of equaliser that divides a stereo signal into mono and stereo channels. The information in the mid (mono) channel is identical to that in the left and right channels. A mono signal is created by adding the left and right channels (L+R=Mid).
- The side (stereo) channel, on the other hand, carries information that differs from the left and right channels. A stereo signal is created by subtracting the left and right channels (L-R=Side). When the mid and side channels are joined, they generate a full stereo field.
- Using an M/S EQ one can process centre information and side information separately. This helps make space in the centre and adds width to the mix.
- L/R EQ - This is used to EQ the left channel and right channel of a stereo channel. You can treat the left channel and right channel separately using L/R EQ.
- Dynamic EQ: Dynamic equalisation (EQ) is a form of equalisation in which the EQ of specific frequencies is activated dynamically when those frequency bands exceed a predetermined amplitude threshold in the audio output. It is a combination of a compressor and an EQ at the same time. Dynamic EQ, like a compressor, will feature threshold, attack, and release parameters to dynamically change the EQ of a signal. Dynamic EQ is a useful tool when EQ-ing out a wide range of frequencies.
EQ plugins and hardware process the signal differently. Analog hardware does not add any delay to the incoming signal while processing it. On the other hand, digital plugins add a negligible amount of delay to the signal while processing it. This is why it is important to use the right EQ processing and avoid issues caused by the extensive use of plugins. Below are the different ways Equalisers process signals: -
Zero Latency Mode: An EQ matches the amplitude response of analogue EQ'ing as precisely as possible in Zero Latency mode, without introducing any latency. It is one of the most efficient processing modes, and it is more than adequate for most tasks but it consumes more CPU processing as well.
Natural Phase EQ: Natural Phase mode is even more effective. It not only perfectly matches the amplitude response of analogue EQ-ing, but it also closely matches the analogue phase response. As a result, it provides the most accurate frequency response and best sound quality, even at the lowest frequencies and highest Q settings, without producing detectable pre-ring or excessive latency.
Linear Phase EQ: Linear-phase filters alter only the magnitude of the audio while leaving the phase alone. These types of EQs are useful when you are EQ-ing with higher magnitude curves and shelves. Keep in mind this processing mode requires heavy processing power as well.
I hope now you have a clear idea of how EQ works. If you have any comments or suggestions please leave them in the comments section below.
In the next lesson learn the Top 10 Equalisation Tips For Beginners That Pro Mix Engineers Don't Want You To Know.