Notes · Music TechnologyUK · A-Levels

Effects and processors

Effects colour, place and transform a sound. This topic sorts them into families and explains insert versus send routing, then works through reverb (recreating a space), delay and ADT (repeats and doubling, synced to tempo), the modulation effects chorus, flanger and phaser (short modulated delays and swept filters), and the harmonic and spectral processors distortion, amp modelling and the vocoder. Throughout, the tempo-to-time and comb-filter numeracy of earlier topics returns.

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

T·131313 / 16

Exam profile

C1 · Route and apply effects using inserts and sends appropriatelyC2 · Use reverb, delay, modulation and harmonic effects creatively and set their parametersC3 · Identify effects by ear and relate their settings to the sound produced

Operators:describeexplainapplycalculateidentify

basic level

The AS foundation is insert vs send, reverb and delay, and the main modulation effects.

higher level

The full A-level adds reverb and delay parameters, tempo-synced delay times, the comb-filter basis of modulation effects, and the vocoder.

Depth

Text

Contents · 5 sections

Effects and processors

Inserts, sends and effect families#

FoundationPearson 9MT0 - effects and processors

Effect families

Fig. 1The effect families by what they do: time-based add space and repeats, modulation add movement, harmonic/amplitude change level and add harmonics, and frequency shape tone.

Effects and processors fall into families by what they do to a signal. Time-based effects (reverb, delay) add repeats and a sense of space. Modulation effects (chorus, flanger, phaser) use a moving delay or filter to add movement and thickness. Amplitude and harmonic processors (distortion, saturation, and the dynamics of the previous topic) change level and add harmonics. Frequency processors (EQ, filters) shape tone. Recognising which family an effect belongs to explains how it works and how it should be routed.

How an effect is connected - as an insert or a send - is a fundamental routing decision. An insert places the effect in series in a single channel, so the whole signal passes through it. Inserts are used for processors that should act on 100% of the signal and belong to that track alone: EQ, compression, gating and distortion are almost always inserts, because you want them to shape the entire sound of that one track.

A send taps a copy of the signal off to a shared effects bus, where the effect processes it in parallel and returns it to the mix, blended with the dry original. Sends are used for time-based effects - reverb and delay - for two reasons: you want to blend a controllable amount of effect with the dry sound (the wet/dry balance), and you want several tracks to share one effect so they sit in the same space, which saves resources and creates coherence.

The wet/dry distinction follows from this. On an insert, the effect's own mix control sets how much processed versus unprocessed signal comes out (often 100% wet for EQ and dynamics). On a send, the send level sets how much of the dry track is fed to the (fully wet) effect bus, and the dry track continues straight to the mix, so the blend is set by the send. Getting reverb and delay onto sends, and EQ and dynamics onto inserts, is the routing that keeps a mix clean and efficient.

For the exam, be able to classify effects into families (time-based, modulation, harmonic/amplitude, frequency), explain insert routing (series, whole signal, per track - for EQ, dynamics, distortion) versus send routing (parallel, shared bus, wet/dry blend - for reverb, delay), and justify which routing suits a given effect. This routing sense underlies every use of the specific effects that follow.

Insert versus send routing

Fig. 2Inserts act in series on the whole of one track (EQ, dynamics, distortion); sends tap a parallel copy to a shared, wet effect bus (reverb, delay) blended with the dry.

Worked example

Routing three effects

Decide insert or send for (a) a compressor on a lead vocal, (b) a hall reverb shared by the vocal and strings, and (c) an overdrive on a bass, and justify each.

The compressor
Insert: compression must act on 100% of the vocal and belongs to that track alone, so it sits in series in the vocal channel.
The shared reverb
Send: a hall reverb on an aux bus, fed by sends from the vocal and strings, blends a controllable amount of a shared space into both for coherence and efficiency.
The overdrive
Insert: distortion should shape the whole bass sound and belongs to that track, so it goes in series as an insert.
The pattern
Time-based (reverb) to a send; tone/level/harmonic processors (compressor, overdrive) to inserts.

Result: Compressor and overdrive as inserts (series, whole signal), the shared hall reverb as a send (parallel, blended, shared) - routing matched to each effect's family.

Typical mistakes

Putting reverb on an insert for every track instead of a shared send, wasting resources and losing a common space.
Putting EQ or compression on a send, where only part of the signal would be processed and blended.

Active revision

State whether you would use an insert or a send for (a) a compressor on a vocal, (b) a hall reverb shared by several tracks, and (c) distortion on a bass, 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)

Reverb#

StandardPearson 9MT0 - effects and processors

The structure of reverb

Fig. 3Reverb recreates a space in three stages: the direct sound, the early reflections (after a pre-delay), and the dense, decaying reverberant tail whose length is the decay time.

Reverb recreates the sound of a space, placing a dry, close-miked source into a room, hall or artificial environment. It recreates the acoustic behaviour of the room-acoustics topic: the direct sound reaches the listener first, then a set of early reflections bounce off nearby surfaces a few milliseconds later, and finally a dense, decaying reverberant tail of thousands of reflections dies away. Reverb adds depth, space, size and glue to otherwise dry recordings.

Reverb comes in several types. A room or hall reverb models a natural acoustic space of a given size. A plate reverb (originally a large vibrating metal plate) gives a smooth, dense, bright tail loved on vocals and snares. A spring reverb (a metal spring, as in guitar amps) has a distinctive boingy character. A convolution reverb captures the actual acoustic 'fingerprint' (impulse response) of a real space or unit and applies it, for highly realistic spaces. Choosing the type sets the character of the space.

The key parameters shape that space. Pre-delay is the gap between the direct sound and the onset of the reverb, and it controls perceived size and keeps the source clear - a longer pre-delay suggests a bigger space and stops the reverb smearing the attack of the dry sound. Decay time (the reverb's RT) sets how long the tail lasts - short for a small room, long for a cathedral. Size, damping (how quickly the highs are absorbed), diffusion and the wet/dry mix complete the control.

Reverb is used both to place a sound in a believable space and as an audible effect. Corrective, realistic use adds a natural room or hall so a dry recording sounds situated; creative use applies long, lush or unusual reverbs as a texture. Because reverb adds level and can build up quickly, it is placed on a send so several sources share one coherent space and the wet amount is easily controlled, and it is often high-passed so it does not muddy the low end.

For the exam, be able to describe reverb's structure (direct sound, early reflections, decaying tail), name the main types (room/hall, plate, spring, convolution) and their characters, and explain the key parameters - pre-delay (size and clarity), decay time (length of tail), damping and mix. Setting a reverb to place a sound at a chosen depth and size, and justifying pre-delay and decay choices, are standard tasks.

Worked example

Placing a vocal in a hall

A lead vocal must sit in a medium hall for depth but keep its words clear. Choose a reverb type and set the pre-delay, decay and mix.

Type
Choose a hall (or a smooth plate) reverb for a musical, dense space appropriate to a lead vocal.
Pre-delay for clarity
Set a pre-delay of around 20-40 ms so the dry vocal's attack is heard clearly before the reverb enters, keeping the words distinct and suggesting a sizeable space.
Decay for size
Set a decay time of roughly 1.5-2 s for a medium hall - long enough for depth, short enough not to wash over the next phrase.
Mix and high-pass
Put the reverb on a send and set a modest wet level; high-pass the reverb return so it does not muddy the low end.

Result: A hall reverb on a send with ~30 ms pre-delay, ~1.5-2 s decay and a modest, high-passed wet level places the vocal in a hall while keeping its words clear.

Typical mistakes

Ignoring pre-delay, so the reverb smears the attack of the source and the source loses clarity and definition.
Putting a long, un-high-passed reverb on everything, muddying the mix; reverb belongs on a send and is often high-passed.

Active revision

Describe the reverb type and the pre-delay and decay settings you would use to place a lead vocal in a medium hall while keeping its words clear.

Active recall

Recall the key points — then reveal.

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

Delay and ADT#

StandardPearson 9MT0 - effects and processors

Delay times and types at 120 bpm

Fig. 4Delay types: a slapback is a short single echo (~110 ms); tempo-synced delays lock to note values (eighth 250 ms, dotted-eighth 375 ms, quarter 500 ms at 120 bpm).

A delay records the signal and plays it back after a set time, producing distinct repeats (echoes). Its three main controls are the delay time (how long before the repeat), the feedback (how much of the output is fed back in, setting the number of repeats - none for a single echo, more for a train that decays away), and the mix (how loud the repeats are against the dry). Delay places a sound rhythmically and adds space, depth and interest.

Delay time is usually set in time with the music, using the tempo-to-milliseconds calculation from the numeracy topic: one beat is 60000/bpm milliseconds, so an eighth-note delay at 120 bpm is 250 ms, a dotted eighth 375 ms, a quarter 500 ms. Synced delays lock the repeats to the groove (the dotted-eighth delay is a staple of guitar and synth parts). Short, un-synced delays create other effects: a slapback delay of about 80-120 ms gives a single quick echo (classic on rockabilly vocals and guitars).

Automatic double tracking (ADT) uses a very short delay (a few tens of milliseconds), often slightly modulated, to create a second, doubled voice from a single take - imitating the thickening effect of a singer recording the same part twice. A short delay under about 30 ms is not heard as a separate echo but fuses with the original (the precedence effect) to thicken and widen it, which is the basis of doubling and of the modulation effects in the next section.

The behaviour depends on the delay time relative to perception. Very short delays (below ~30 ms) fuse with the dry sound and thicken it (ADT, and comb-filter effects); medium delays (roughly 30-100 ms) give a slapback echo; longer, tempo-synced delays give rhythmic repeats. Feedback turns a single repeat into a decaying train, and filtering the repeats (darker with each pass) makes the echoes recede naturally, as in a tape or analogue delay.

For the exam, be able to describe delay's controls (time, feedback, mix), calculate a tempo-synced delay time from the bpm, distinguish slapback (a short single echo) from rhythmic synced delays, and explain ADT (a very short delay that doubles and thickens a single take). The tempo-to-time calculation and the perceptual thresholds (fuse, slapback, echo) are the examinable core.

Worked example

A tempo-synced delay

At 100 bpm, set a delay for a syncopated dotted-eighth repeat on a synth lead. Calculate the delay time and describe the feedback and mix.

Beat length
One beat = 60000/bpm = 60000/100 = 600 ms.
Dotted eighth
A dotted eighth is three-quarters of a beat: 600 x 0.75 = 450 ms (equivalently an eighth of 300 ms times 1.5).
$600 \times \tfrac{3}{4} = 450\,\text{ms}$
Feedback
Set a moderate feedback so the repeats form a short decaying train (a few audible echoes) rather than one repeat or an endless loop.
Mix
Put the delay on a send and set the wet level so the repeats support the lead without overwhelming it; filter the repeats darker for depth.

Result: A 450 ms dotted-eighth delay at 100 bpm gives the syncopated repeat; moderate feedback and a modest, filtered wet level place it behind the lead.

Typical mistakes

Confusing feedback (number of repeats) with mix (level of the repeats) - they are separate controls.
Thinking any delay is heard as an echo - below about 30 ms the delay fuses with the dry sound and thickens it instead.

Active revision

At 100 bpm, calculate the delay time in milliseconds for an eighth-note and a dotted-eighth delay, and state which produces the classic syncopated repeat.

Active recall

Recall the key points — then reveal.

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

Modulation effects: chorus, flanger, phaser#

StandardPearson 9MT0 - effects and processors

How a modulation effect works

Fig. 5Chorus and flanger work by summing the dry signal with a short, LFO-modulated delayed copy: the sum comb-filters, and the LFO sweeps the comb for movement (chorus long delay, flanger very short).

The modulation effects add movement by using an LFO to modulate a short delay (or a filter) and mixing the result with the dry signal. Because a delayed copy summed with the original produces comb filtering (peaks and notches across the spectrum), and the LFO makes that comb sweep up and down, the effect is a moving, swirling colouration. Chorus, flanger and phaser are the three, distinguished mainly by their delay times and mechanism.

Chorus uses a moderately short delay (around 15-35 ms), pitch-modulated by an LFO, mixed with the dry sound, to imitate several performers playing together - the slight, ever-changing differences in timing and pitch between copies thickening and widening the sound into an ensemble. It is lush and subtle, used to fatten guitars, keyboards and vocals without an obvious swirling.

Flanger uses a much shorter delay (around 1-10 ms) swept by an LFO and mixed with the dry, producing a strong, sweeping comb filter - the characteristic 'jet plane' whoosh. Adding feedback intensifies the resonant peaks for a more metallic, dramatic sweep. Because the delay is so short, the comb notches are widely spaced and move audibly as the delay time sweeps, which is the flanger's signature sound.

Phaser works differently: instead of a delay, it passes the signal through a series of all-pass filters that create notches in the spectrum, and an LFO sweeps those notches up and down. Mixed with the dry, this gives a softer, swooshing, less metallic movement than a flanger. The number of filter stages sets how many notches and how rich the effect. So chorus (longer delay, pitch-modulated - thickening), flanger (very short delay - sweeping comb) and phaser (swept all-pass notches - swoosh) form a family of movement effects.

For the exam, be able to describe how chorus, flanger and phaser each create their movement (chorus: ~15-35 ms pitch-modulated delay for thickening; flanger: ~1-10 ms swept delay for a comb-filter jet; phaser: swept all-pass notches for a swoosh), and relate them to the comb-filter idea. Distinguishing the three by their delay time and mechanism, and by ear, is the examinable skill.

Worked example

Chorus versus flanger on a guitar

Set a chorus to thicken a clean guitar, then explain how a flanger on the same guitar would differ.

Chorus delay and modulation
Use a delay of about 15-35 ms, pitch-modulated by a gentle LFO, mixed with the dry guitar, so the copy drifts slightly in time and pitch to imitate a second player - thickening and widening the sound.
Chorus settings
Set a slow LFO rate and modest depth for a subtle ensemble effect rather than an obvious wobble.
How a flanger differs
A flanger uses a much shorter delay (about 1-10 ms) swept by the LFO, so the comb-filter notches are widely spaced and sweep audibly, giving the metallic 'jet plane' whoosh rather than a gentle thickening.
Feedback
Adding feedback to the flanger intensifies its resonant sweep, a control the subtle chorus does not emphasise.

Result: A ~15-35 ms pitch-modulated chorus thickens the guitar like an ensemble; a flanger's ~1-10 ms swept delay instead gives a metallic jet whoosh.

Typical mistakes

Confusing flanger and phaser - the flanger uses a swept short delay (comb filter), the phaser uses swept all-pass filter notches.
Thinking chorus and flanger differ only in intensity - their delay times differ greatly (chorus much longer than flanger).

Active revision

Explain, in terms of delay time and mechanism, how you would set a chorus to thicken a clean guitar and how a flanger differs from it.

Active recall

Recall the key points — then reveal.

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

Distortion, amp modelling and the vocoder#

AdvancedPearson 9MT0 - effects and processors

The vocoder

Fig. 6The vocoder: an analysis filterbank measures the voice's (modulator's) formants band by band, and those envelopes shape a synthesis filterbank on the synth (carrier) - the synth speaks with the voice's articulation.

Distortion changes a sound by clipping or reshaping its waveform, which adds new harmonics and so changes the timbre - making it richer, dirtier or more aggressive. Gentle overdrive and saturation (as from a valve or tape) add warmth and subtle harmonics that thicken a sound; harder distortion and fuzz clip the waveform heavily for an aggressive, buzzy tone. Because distortion adds harmonics, it interacts with EQ and can make a thin sound fuller or a dull one bright, and it is applied as an insert on the whole signal.

Amp modelling (amp simulation) recreates the sound of guitar and bass amplifiers, speaker cabinets and microphones in software. A real electric guitar's sound is shaped enormously by its amp and cab, so amp modelling lets a DI'd guitar be given a convincing amplified tone in the box - choosing the amp type, gain (overdrive), tone controls and a virtual cabinet and microphone. It packages distortion, EQ and cabinet resonance into a single, musically-organised effect.

The vocoder is a distinctive spectral effect that imposes the changing tone of one sound (the modulator, usually a voice) onto another (the carrier, usually a synth), producing the classic 'talking synth' or robot-voice. It works with two filterbanks: an analysis filterbank measures the energy in many frequency bands of the modulator (the voice's formants and their movement), and those measurements control a synthesis filterbank shaping the carrier, so the synth 'speaks' with the voice's articulation while keeping the synth's pitch and timbre.

These processors are creative sound-design tools central to the technology-based composition. Distortion and saturation add colour and aggression; amp modelling gives virtual guitar and bass tones; the vocoder turns a voice and a synth into a talking instrument. Each transforms the harmonic or spectral content of a sound rather than its level (dynamics) or space (reverb/delay), completing the palette of processing available to a producer.

For the exam, be able to explain distortion/saturation as harmonic-adding waveform clipping (overdrive/fuzz), describe amp modelling as software simulation of amps, cabs and mics for guitar/bass tone, and explain the vocoder as imposing a modulator's (voice's) formants onto a carrier (synth) via two filterbanks. Understanding the vocoder's carrier/modulator structure, and that distortion adds harmonics, are the examinable points.

Worked example

Making a talking synth

Set up a vocoder to make a synth pad 'speak' the words of a spoken vocal. Identify the carrier and modulator and describe how it works.

Assign the modulator
The spoken voice is the modulator: it supplies the changing formants (the vowel and consonant shapes) that carry the words.
Assign the carrier
The synth pad is the carrier: it supplies the pitch and harmonic-rich tone that the effect will shape - a bright, sustained waveform (sawtooth) works well.
How it works
The analysis filterbank measures the energy in many bands of the voice; those band envelopes control the synthesis filterbank shaping the carrier, so the pad takes on the voice's articulation while keeping the synth's pitch and character.
Result
The synth pad appears to speak the words, at whatever pitch is played - the classic talking-synth/robot-voice effect.

Result: The voice (modulator) imposes its formants, via the analysis filterbank, onto the synth pad (carrier) through the synthesis filterbank - the pad speaks the words.

Typical mistakes

Thinking distortion only makes a sound louder - it adds harmonics and reshapes the waveform, changing the timbre.
Reversing the vocoder's roles - the voice is the modulator (supplies the formants); the synth is the carrier (supplies the tone).

Active revision

Explain what a vocoder needs as its carrier and its modulator to make a 'talking synth', and describe how the effect is produced.

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)

Effects and processors

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

Effects and processors

Key points

Routing three effects

Key points

Placing a vocal in a hall

Key points

A tempo-synced delay

Key points

Chorus versus flanger on a guitar

Key points

Making a talking synth

Sources

Effects and processors

Key points

Routing three effects

Key points

Placing a vocal in a hall

Key points

A tempo-synced delay

Key points

Chorus versus flanger on a guitar

Key points

Making a talking synth

Sources