Notes · Music TechnologyUK · A-Levels

EQ and frequency shaping

Equalisation (EQ) boosts or cuts chosen frequency regions to shape the tone of a sound and carve space in a mix. This topic sets EQ against the frequency spectrum, then builds up the tools: pass filters and their slope, shelving and bell curves, the full parametric EQ with its gain, frequency and Q controls (including the narrow notch that removes mains hum), and the fixed-band graphic EQ. It closes with the practical judgement of corrective versus creative EQ.

5 sections~19 min reading time3 competenciesLevel Foundation 1 · Standard 3 · Advanced 1

T·121212 / 16

Exam profile

C4 · Shape tone and solve mix problems with pass, shelf, bell, parametric and graphic EQC4 · Set gain, frequency, Q and slope and read an EQ response curveC1 · Apply corrective and creative EQ with judgement

Operators:describeexplainapplydeterminejustify

basic level

The AS foundation is what EQ does, pass filters, and shelving and bell EQ.

higher level

The full A-level adds Q and bandwidth, the parametric notch, graphic EQ and corrective-versus-creative judgement.

Depth

Text

Contents · 5 sections

EQ and frequency shaping

EQ and the frequency spectrum#

FoundationPearson 9MT0 - EQ and frequency shaping

EQ regions across the spectrum

Fig. 1The spectral map for EQ: weight in the bass, mud in the low-mids, body in the mids, presence and bite in the upper-mids, and air at the top - the language of EQ moves.

Equalisation is the boosting or cutting of chosen frequency regions of a signal, and it is the most-used tone-shaping tool in production. Because every sound is a blend of frequencies (a fundamental and its harmonics), changing the balance of those frequencies changes the tone: cutting the lows thins a sound, boosting the highs brightens it, dipping the mids hollows it. EQ is therefore how a recordist corrects tonal problems, enhances the character of a sound, and makes many instruments coexist in a mix.

To use EQ you must know roughly where things live in the spectrum. The low end (sub-bass and bass, below about 250 Hz) carries weight and power; the low-mids (250-500 Hz) carry warmth but also 'mud' and 'boxiness' when built up; the mids (500 Hz-2 kHz) carry body and the fundamentals of many instruments; the upper-mids or presence (2-6 kHz) carry attack, intelligibility and bite (and harshness); and the highs (6-20 kHz) carry air, sparkle and sibilance. Learning these descriptors lets you translate a heard problem into an EQ move.

A key mix use of EQ is to carve space so instruments do not mask one another. Because masking is worst when sounds share the same frequency band (from the psychoacoustics topic), gently cutting one instrument where another needs to be heard - dipping a guitar where the vocal's presence sits, or the bass where the kick's thump lives - lets each occupy its own region. This 'complementary' EQ is often more effective than boosting, because it removes the clash at its source.

EQ decisions are guided by the ear and by knowledge of the source. A muddy mix usually needs a cut in the low-mids; a dull vocal a lift in the presence region; a boomy room a high-pass or a low-mid dip; a harsh cymbal a cut around 3-5 kHz. The frequency descriptors give a starting point, but the exact frequency and amount are set by listening. EQ is thus a translation between what you hear and where in the spectrum to act.

For the exam, be able to explain what EQ does (boost/cut frequency regions to shape tone and carve space), locate the broad spectral regions and their sonic descriptors (mud in the low-mids, presence in the upper-mids, air at the top), and describe how complementary EQ reduces masking. This spectral map underlies every specific EQ tool in the sections that follow.

Worked example

Translating problems into EQ regions

A mix is muddy, its vocal is dull, and a cymbal is harsh. State the region and the move (cut or boost) for each.

Muddy mix
Mud lives in the low-mids; cut around 250-400 Hz on the offending track(s) to clear it.
Dull vocal
Intelligibility and air sit in the presence region; a gentle boost around 3-5 kHz (and a little high-shelf air) brightens the vocal.
Harsh cymbal
Harshness sits in the upper-mids; a narrow cut around 3-5 kHz tames the cymbal without dulling its sparkle.
Prefer cuts
Two of the three are cuts, reflecting that removing an offending region is often cleaner than boosting and helps reduce masking.

Result: Cut ~300 Hz for the mud, boost ~4 kHz for the dull vocal, cut ~4 kHz for the harsh cymbal - heard problems mapped to spectral moves.

Typical mistakes

Reaching for a boost to fix every problem - cutting the offending region (or a competing instrument) is often cleaner and reduces masking.
Not knowing the spectral descriptors, so a heard problem ('muddy', 'harsh', 'dull') cannot be turned into an EQ move.

Active revision

Name the approximate frequency region you would address to fix (a) a muddy mix, (b) a dull, unintelligible vocal, and (c) a harsh cymbal, and say whether you would cut or boost.

Active recall

Recall the key points — then reveal.

Sources: Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification (Pearson Edexcel)

Filter types: high-pass, low-pass and band-pass#

StandardPearson 9MT0 - EQ and frequency shaping

High-pass and low-pass filter responses

Fig. 2A high-pass passes frequencies above the cut-off (removing lows); a low-pass passes those below it (removing highs). The slope sets how steeply each rolls off.

The simplest EQ tools are pass filters, which remove a whole region of the spectrum. A high-pass filter (also called a low-cut) passes the frequencies above its cut-off and progressively removes those below it - used to strip rumble, plosives and unnecessary low end from a track (a vocal, a hi-hat) so the low frequencies belong only to the instruments that need them. A low-pass filter (high-cut) does the opposite, passing lows and removing highs above its cut-off, used to tame hiss, fizz or brightness.

The band-pass filter combines the two, passing only a band of frequencies around a centre and removing everything above and below - useful for telephone or lo-fi effects and for isolating a band. These pass filters differ from the boost/cut EQs of the next sections in that they remove a region entirely rather than adjusting its level, so they are the tools for cleaning up and for dramatic tonal effects.

The cut-off frequency is where the filter reaches a defined attenuation (conventionally the -3 dB point), and the slope (or order) sets how steeply it removes frequencies beyond that - measured in decibels per octave. A gentle 6 dB/octave slope removes the region gradually and transparently; a steep 24 dB/octave slope removes it sharply and decisively. A steeper slope is more surgical but can sound less natural, so the slope is chosen for the job: gentle for subtle cleanup, steep for a hard cut.

The everyday use of the high-pass filter is worth stressing: applying a high-pass around 80-120 Hz to every track that carries no useful low end (most vocals, guitars, cymbals) removes rumble and low-frequency build-up and dramatically cleans a mix, leaving the bottom to the bass and kick. This single habit solves much of the 'muddy mix' problem before any other EQ, provided the cut-off is kept below each source's useful low frequencies.

For the exam, be able to describe the high-pass (low-cut), low-pass (high-cut) and band-pass filters and what each removes, explain the cut-off frequency and the slope in dB/octave, and give the practical use of a high-pass to clean low-frequency clutter from a mix. Reading a filter response - identifying the passband, the cut-off and the slope - is a standard skill.

Worked example

High-passing a vocal

A vocal track carries floor rumble and low-frequency mud but the voice itself has nothing useful below about 100 Hz. Choose the filter, cut-off and slope.

Choose the filter
Use a high-pass (low-cut) filter, which passes the voice above the cut-off and removes the rumble below it.
Set the cut-off
Set the cut-off around 90-100 Hz, below the voice's useful low frequencies, so the rumble is removed without thinning the voice.
Choose the slope
A moderate slope (12-18 dB/octave) removes the rumble decisively while sounding natural; a very steep slope is unnecessary here.
Check
Solo the vocal and confirm the rumble is gone and the voice's warmth is intact; nudge the cut-off down if the voice thins.

Result: A high-pass filter around 90-100 Hz at a moderate slope removes the rumble and mud while leaving the voice's body untouched.

Typical mistakes

Confusing high-pass (removes lows, passes highs) with low-pass (removes highs, passes lows) - the name refers to what passes.
Setting a high-pass cut-off too high, thinning the useful low end of the source along with the rumble.

Active revision

State which pass filter, and roughly what cut-off and slope, you would use to remove low-frequency rumble from a vocal track without thinning the voice.

Active recall

Recall the key points — then reveal.

Sources: Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification (Pearson Edexcel)

Shelving and bell (peak) EQ#

StandardPearson 9MT0 - EQ and frequency shaping

Shelf and bell EQ curves

Fig. 3A low shelf boosts everything below its corner (a plateau); a bell boosts a band around a centre frequency, tapering off either side. The bell's width is set by its Q.

Where pass filters remove a region, boost/cut EQs adjust its level, and the two basic shapes are the shelf and the bell. A shelving EQ boosts or cuts everything beyond a chosen frequency by a set amount, forming a plateau (a shelf). A low shelf lifts or lowers all the frequencies below its corner (adding or reducing weight and warmth); a high shelf does the same above its corner (adding air and brightness or taming harshness). Shelves are broad, gentle and musical, ideal for overall tonal tilt.

A bell (or peak/dip) EQ boosts or cuts a band centred on a chosen frequency, tapering off above and below - a hump for a boost or a dip for a cut. Unlike a shelf, it acts only around its centre frequency, leaving the extremes unchanged, so it is the tool for targeting a specific region: boosting the presence of a vocal at 4 kHz, dipping the mud of a guitar at 300 Hz, lifting the thump of a kick at 60 Hz. Most EQ moves in a mix are bell boosts and cuts.

The bell has three parameters: the frequency (where its centre sits), the gain (how much boost or cut, in decibels) and the Q (how wide or narrow the band is). A low Q gives a wide, gentle bell that affects a broad range musically; a high Q gives a narrow, surgical bell that targets a precise frequency - useful for removing a specific resonance or ringing note. Learning to set frequency, gain and Q together is the core skill of bell EQ.

Shelves and bells suit different jobs. Use a shelf for broad tonal shaping - a high shelf to add air across the whole top end, a low shelf to add or trim overall weight. Use a bell to target a specific problem or feature - a narrow cut to remove a resonance, a moderate boost to enhance a particular region. Many EQs let a band switch between shelf and bell shapes, so choosing the right shape for the move is itself a decision.

For the exam, be able to describe the low and high shelf (a plateau boost/cut beyond a corner frequency) and the bell/peak (a boost/cut around a centre frequency), explain the bell's frequency, gain and Q controls, and choose the right shape for a task (shelf for broad tilt, bell for targeted moves). Reading these shapes off an EQ response curve is regularly required.

Worked example

Choosing shelf or bell

You want to (a) add a smooth sense of air across the whole top of a mix and (b) remove a specific resonant ring at 500 Hz on a snare. Choose the EQ shape and settings for each.

The air
Use a high shelf: set its corner around 10 kHz and boost a few decibels so the entire top end lifts smoothly for air, rather than a single band.
The resonant ring
Use a bell (dip): set the frequency to 500 Hz, a negative gain to cut it, and a high Q so the cut is narrow and surgical, removing the ring without dulling the surrounding sound.
Why these shapes
The air is a broad tilt (a shelf's job), the ring is a single precise frequency (a narrow bell's job).
Confirm
Sweep to find the exact ring frequency first, then narrow the Q and cut; check the snare keeps its body.

Result: A high shelf around 10 kHz adds broad air; a narrow high-Q bell cut at 500 Hz removes the specific ring - shape matched to the move.

Typical mistakes

Confusing a shelf (affects everything beyond a corner) with a bell (affects only a band around a centre).
Using a very high Q for broad tonal shaping, producing an unnatural, ringing boost instead of a smooth shelf.

Active revision

State whether a shelf or a bell, and roughly what frequency, you would use to (a) add overall air to a mix and (b) remove a specific resonant ring at 500 Hz.

Active recall

Recall the key points — then reveal.

Sources: Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification (Pearson Edexcel)

Parametric EQ: gain, frequency and Q#

StandardPearson 9MT0 - EQ and frequency shaping

Parametric notches on mains hum

Fig. 4A parametric notch is a high-Q, deep cut. Tuned exactly to 50 Hz and its harmonic at 100 Hz (UK mains), it removes the hum while barely touching the surrounding music.

A parametric EQ gives full, independent control over each band's three parameters - the centre frequency, the gain (boost or cut) and the Q (bandwidth) - and usually offers several bands plus pass filters and shelves. This flexibility makes it the most powerful and precise EQ, able to target any region with any width and amount, which is why it is the standard EQ for detailed corrective and creative work in the DAW and in Component 4 tasks.

The Q control deserves careful understanding because it sets the width of a band. Q (quality factor) is inversely related to bandwidth: a high Q gives a narrow band affecting a small range of frequencies, a low Q a wide band affecting a broad range. The bandwidth in octaves narrows as Q rises, so a high-Q boost or cut is surgical while a low-Q one is broad and gentle. Choosing Q with the frequency and gain is what distinguishes a musical, transparent move from a clumsy or a surgical one.

A high-Q, deep cut is called a notch (band-reject) filter, and it removes a very narrow band almost entirely - the ideal tool for eliminating a single problem frequency without touching the rest of the sound. The classic use is removing mains hum: because hum sits at exact, known frequencies (50 Hz in the UK and its harmonics 100, 150 Hz; 60 Hz in North America and 120, 180 Hz), narrow notches tuned precisely to those frequencies remove the hum while leaving the music essentially untouched.

Using a parametric EQ well follows a method. To find a problem frequency, boost a bell with a high Q and sweep its frequency across the range until the problem (a resonance, a ring, harshness) leaps out, then turn the gain to a cut and narrow the Q to remove just that frequency - the 'boost, sweep, cut' technique. For creative shaping, broader Q boosts enhance a region's character. The parametric EQ's precision rewards this systematic approach.

For the exam, be able to describe the parametric EQ's independent gain, frequency and Q controls, explain that Q sets the bandwidth (high Q narrow, low Q wide), and describe the notch as a high-Q deep cut for removing exact problem frequencies such as mains hum. Being able to specify the settings to notch out 50/60 Hz hum, and to use the boost-sweep-cut method, are standard high-value skills.

Worked example

Notching out mains hum

A UK vocal recording has an audible 50 Hz mains hum with harmonics. Specify the parametric EQ settings to remove it cleanly.

Identify the frequencies
UK mains hum is at 50 Hz with harmonics at 100 Hz, 150 Hz (and possibly 200 Hz); these exact frequencies are the targets.
Set the notches
Create a band at 50 Hz with a deep cut (around -20 dB or more) and a high Q (narrow bandwidth) so only the hum is removed; repeat at 100 and 150 Hz.
Keep them narrow
A high Q is essential: a wide cut would remove musical low-frequency content around 50 Hz as well, but a narrow notch takes only the hum tone.
Country check
Note that a North American recording would use 60 Hz and its harmonics (120, 180 Hz) instead - always tune to the local mains frequency.

Result: Narrow high-Q notches with deep cuts at 50, 100 and 150 Hz remove the UK mains hum and its harmonics while leaving the music intact (60/120/180 Hz in North America).

Typical mistakes

Thinking a higher Q gives a wider band - a higher Q gives a narrower band (smaller bandwidth).
Notching hum with a wide, low-Q cut, which removes musical content around 50/60 Hz as well; the notch must be narrow (high Q).

Active revision

A UK recording has a 50 Hz mains hum. Describe the exact parametric EQ settings (frequency, gain, Q) to remove it and its main harmonics without harming the music.

Active recall

Recall the key points — then reveal.

Sources: Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification (Pearson Edexcel)

Graphic EQ and practical EQing#

AdvancedPearson 9MT0 - EQ and frequency shaping

EQ types and their uses

Fig. 5The EQ family: pass filters remove a region; shelves tilt broad bands; bells target a band; the parametric gives full control; the graphic offers fixed-band visual control.

A graphic EQ divides the spectrum into a fixed set of bands - each a slider at a set frequency - so its response is drawn out visually by the positions of the sliders. A common form is a 31-band, one-third-octave graphic used for tuning live systems and rooms. Its advantage is a quick visual overview and hands-on control of many bands; its limitation is that the band frequencies and their Q are fixed, so it cannot target an arbitrary frequency or width as a parametric can.

The graphic and parametric EQs represent a trade-off between overview and precision. The graphic is fast and intuitive for broad, many-band shaping (taming a room, sculpting a broad tone) but coarse; the parametric is precise and flexible for surgical, targeted work but shows less at a glance. Knowing which to reach for - graphic for a broad, visual, many-band tilt; parametric for a specific, precise move - is part of practical EQ skill.

Practical EQ is guided by a few principles. Subtractive EQ - cutting problem frequencies - is often preferable to boosting, because it solves the problem at source, adds no level, and reduces masking; cut to fix, boost to enhance. EQ in context, not in solo, because a sound that seems dull alone may be perfectly placed in the mix, and a solo-perfect EQ can clash. And EQ with purpose: each move should solve a heard problem or serve a deliberate character, not be applied by habit.

Corrective and creative EQ are the two modes, echoing the corrective-versus-creative theme of the subject. Corrective EQ fixes problems transparently - removing mud, hum, harshness or resonance so the sound is naturally right (Component 4). Creative EQ deliberately colours a sound - a telephone band-pass, an extreme low-fi cut, a heavy tonal tilt - as an effect (Component 2). The tools are the same; the intent differs.

For the exam, be able to describe the graphic EQ (fixed bands as sliders, a visual overview, coarse) and contrast it with the parametric (flexible, precise), and to state the practical principles: prefer cuts, EQ in context, EQ with purpose, and distinguish corrective from creative EQ. A tree of the EQ types and their uses is a useful summary, and choosing the right EQ for a task is regularly assessed.

Worked example

Graphic or parametric?

Choose the right EQ for (a) quickly reducing feedback across a live PA system and (b) removing one precise ringing frequency from a recorded tom.

The live PA
Use a graphic EQ: its many fixed bands as sliders give a fast, visual way to pull down the several frequencies that feed back across the whole system.
The tom ring
Use a parametric EQ: sweep a high-Q bell to find the exact ringing frequency, then cut it with a narrow notch - precision the graphic's fixed bands cannot match.
The trade-off
The graphic wins on speed and overview across many bands; the parametric wins on precisely targeting one frequency and width.
Conclude
Match the tool to the task: broad, fast, many-band work to the graphic; precise, single-frequency work to the parametric.

Result: A graphic EQ for the fast, many-band PA taming and a parametric EQ for the one precise tom resonance - overview versus precision.

Typical mistakes

Assuming a graphic EQ can target any frequency - its bands and Q are fixed; a parametric is needed for precise targeting.
EQing a track in solo until it sounds good alone, then finding it no longer fits the mix.

Active revision

State whether a graphic or a parametric EQ suits (a) quickly taming feedback across a live PA and (b) removing one precise resonant frequency from a recorded tom, and justify each.

Active recall

Recall the key points — then reveal.

Sources: Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification (Pearson Edexcel) · Ofqual - GCE AS and A level qualifications (subject-level conditions and requirements) (Ofqual)

References & sources

Sources

Pearson Edexcel

Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification

Ofqual

Ofqual - GCE AS and A level qualifications (subject-level conditions and requirements)

EQ and frequency shaping

5 sections~19 min reading time3 competenciesLevel Foundation 1 · Standard 3 · Advanced 1

EQ and frequency shaping

Key points

Translating problems into EQ regions

Key points

High-passing a vocal

Key points

Choosing shelf or bell

Key points

Notching out mains hum

Key points

Graphic or parametric?

Sources

EQ and frequency shaping

Key points

Translating problems into EQ regions

Key points

High-passing a vocal

Key points

Choosing shelf or bell

Key points

Notching out mains hum

Key points

Graphic or parametric?

Sources