We all know sound/audio basically is measured in dB, But however, every single sound you hear falls under at least one category under the Audio frequency spectrum. Meaning the frequency spectrum is split into different parts.
WHAT IS THE AUDIO FREQUENCY SPECTRUM?
Basically, The audio frequency spectrum is the audible frequency range at which humans can hear. It is measured in Hz.
Humans can hear/detect sounds in the frequency range of 20Hz to 20000Hz
(Human infants can actually hear frequencies slightly higher than 20 kHz, but lose some high-frequency sensitivity as they mature; Animals like dogs however can hear from about 40Hz to about 50000Hz, which means, dogs can hear some sounds humans can't.)
RELATIONSHIP BETWEEN EQ AND AUDIO FREQUENCY SPECTRUM
Firstly, understanding the Audio frequency spectrum is key to EQ’ing. As aforementioned, the Audio Frequency Spectrum represents frequency values of where each sound falls into.
EQ however is short for the term EQUALIZATION.
Equalization or EQ is a piece of hardware or software plugin, that allows one to directly affect/adjust the volume level of a frequency (or range of frequencies) within a sound, which in turn allows you to correct a sound, or sometimes even entire mixes. EQ achieves this using frequency bands broken down into different sections in accordance with the frequency spectrum.
FREQUENCY SPECTRUM BREAKDOWN
The human frequency range (20Hz — 20000Hz)is divided into 3 main divisions;
- Low End/Bass (20Hz–500Hz)
- Midrange (500Hz — 4000Hz)
- High End/Treble (4000Hz — 20000Hz)
However, these 3 can further be split into 7 namely;
- Sub-Bass
- Bass
- Low Midrange
- Midrange
- Upper-Midrange
- Presence
- Brilliance
- Sub-Bass: This consists of frequencies between 20Hz-60Hz. The bass in this range is often felt more than heard, providing a sense of power.
(However, It is recommended that no or very little equalization boost is applied to this region without the use of very high-quality monitor speakers/headphones. i.e too much boost makes the sound overly powerful, whereas too much cut could weaken and thin out the sound.)
2. Bass: This ranges between 60Hz-250Hz. Basically, it determines how fat or thin the sound is. Properly using EQ here tends to determine the low-end definition; how punchy/boomy the sound is.
The frequencies around 250 Hz can add a feeling of warmth to the bass without loss of definition as well as significant cuts can cause loss of definition.
Too much boost here tends to make the music sound overly boomy.
3. Low Midrange: The lower midrange consists of frequencies between 250Hz-500Hz. It could be viewed as the Bass presence range, it contains the lower harmonics of most instruments.
Usually, slight boosts around 300Hz adds clarity to the bass and other lower-end instruments, but in most cases excessive boosts in this range causes the sound/mix to become/sound muddy.
4. Midrange: This ranges from 500Hz to 2000Hz and it is referred to as the center frequency range or midrange. This is an important range where the content of dialogue, vocals, and film & TV sound effects reside.
Boosting around 1000Hz can give instruments a horn-like quality. Cheaper headphones, speakers, and mobile phones focus the majority of their output in this range.
5. Upper Midrange: This is between 2000Hz to 4000Hz. This section is a delicate part of a sound, instrument or a mix in general. The slightest boost or cut can result in a huge change the sound timbre. The high midrange can be related to the attack on sounds like percussive and rhythm instruments. Vocals are also quite prominent in this range.
Too much boost around 3000Hz often causes listening fatigue.
6. Presence: The presence range is about 4000Hz — 6000Hz. It is is responsible for the clarity and definition of a sound.
When dealing with vocals: it is the area where sibilance is heard.
When dealing with mixes/instruments: it adds qualities such as warmth and sweetness to high strings, synths, orchestral music, and other high-end instruments. If overdone it adds harshness and sibilants, not just to vocals, but also cymbals and hi-hats.
It also is the range at which most home stereos center their treble control.
7. Brilliance: 6000Hz — 20000Hz: As the name implies, the brilliance range adds brilliance and high-end clarity to the mix/music. This section is associated with terms like: Detail, Sparkle, and Air.
The 10000Hz affects High-end clarity/detail, and anything above 10000Hz is called Air. Be careful of over-boosting in this region as it can cause unwanted air and increase hiss or cause ear irritations/distractions.
Summary
In conclusion, An EQ is used to directly affect a section or multiple sections of the Audio Frequency Spectrum, overall resulting in a general change in how the sound is perceived.
NB: An effective tip in using EQ better and having better mixes is avoiding multiple instruments with clashing frequencies.
For example
Some high-end/midrange instruments (even vocals) might have frequencies bleeding into the low end and automatically clouding other instruments or elements in the low end such as Kick/808’s. This causes a masking effect and can simply be avoided using a Highpass(Lowcut) Filter and or a Lowpass (Highcut) Filter on every single track on the mixer channel or on group/sub-buses.
i.e On Low-end instruments or elements (such as a kick drum) apply Lowpass (Highcut) Filter to avoid frequencies bleeding into the midrange/high-end, and
On High-end/Midrange instruments or elements (such as snare drum, vocals, some synths and some other instruments) apply Highpass(Lowcut) Filter to avoid frequencies bleeding into the Low-end.
