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Delay lines, comb filters, and modulation effects

L2First instrument 4h B · Sound design & synthesis 22 atoms

Learning objectives

learner can build a delay line with feedback and predict its behavior — echoes, comb-filter coloration, DC accumulation
learner can create slapback, chorus, and flanger effects from modulated delay lines with the right delay-time ranges
learner can use delays and effects as constituent synthesis elements, not just post-processing

Capstone — one whole task that evidences the objectives

From a single modulated delay line, produce four effects — a slapback echo, a chorus, a flanger, and a resonant comb tone — and explain each in terms of delay time, feedback, and modulation.

Prerequisite modules

In a live set, the delay is often the instrument: a dub techno chord is nothing without its feedback tail, and the same delay line that echoes a stab can, at shorter times, become the tone itself. This module builds toward one whole task — running a single modulated delay and steering it, live, between four distinct identities: slapback echo, chorus, flanger, and resonant comb tone. The payoff on stage is real: one UGen or device, one set of parameters, four sounds you can morph between without touching your synth patch.

Start supported. First understand the mechanism — a circular buffer read behind a rotating write pointer — then close the loop and predict the echo train from the feedback gain. From there the arc is about shrinking the delay time and watching perception flip: below the Haas zone (~25–35 ms), repeats fuse into timbre, and the comb-filter spectrum atom explains the evenly-spaced peaks and nulls you now hear. Add an LFO and consult the delay-range fact — 1–20 ms for flanger, 20–30 ms for chorus, 10–120 ms for slapback — as a just-in-time recipe card; the modulated-delay concept ties the whole family together. Keep the DC-accumulation warning nearby whenever feedback climbs.

The required atoms gate the capstone directly: you cannot explain four effects from one delay line without the buffer model, the feedback arithmetic, the comb spectrum, and the canonical time ranges. Supporting atoms enrich by rig and genre — the phaser as a sibling modulation effect built on phase shift rather than a delay buffer, SuperCollider’s Comb family and server memory settings if you’re live-coding, Surge’s BBD ensemble and pitch-tuned comb if you’re patching, dub Echo tricks and noise-fed delay washes if you’re building atmosphere. The overarching principle: effects are synthesis elements, not garnish.

Runnable examples

Generated from the context/ instrument corpus by concept (redistributable idioms only). Do not edit — regenerate with gen-module-examples.mjs.

delay-throw

delay 1 0.375 (osc 330 * lfsqr 2) >> audio

_{punctual-0012 · CC0-1.0}

d1 $ off 0.125 (# speed 2) $ sound "bd sn"

_{tidal-0042 · CC0}

vibrato

saw (midicps $ 24 +- 0.03 $ osc 6) >> audio

_{punctual-0005 · CC0-1.0}

{ SinOsc.ar(SinOsc.kr(6).range(430, 450), 0, 0.2) }.play

_{supercollider-0006 · CC0}

feedback-loop

{ CombN.ar(Impulse.ar(2) * 0.3, 0.2, 0.2, 3) }.play

_{supercollider-0015 · CC0}

s("cp").delay(0.5).delaytime(0.166).delayfeedback(0.7)

_{strudel-0018 · CC0}

physical-modeling

Mandolin m => dac; 0.9 => m.pluck; 220 => m.freq;

_{chuck-0043 · MIT}

Atoms in this module

Required — these gate the capstone

A delay line is a circular buffer read behind a rotating write pointer

Concept L2 First instrument BJ

Adding feedback to a delay line creates decaying echoes whose rate is set by the gain multiplier

Concept L2 First instrument BD

A delay line feeding back into itself creates a comb filter with resonant peaks at integer multiples of 1/delay

Concept L2 First instrument BE

Summing a signal with a delayed copy creates a comb filter: evenly-spaced spectral peaks and nulls set by the delay time

Concept L3 Craft BD

DC offset accumulates in feedback delay loops and must be filtered with a sub-audio highpass

Concept L2 First instrument BD

Flanger uses 1-20 ms LFO-modulated delay; chorus uses 20-30 ms; slapback uses 10-120 ms

Fact L1 Foundations BD

A single modulated delay line produces chorus, flanger, and vibrato depending on its delay-time settings

Concept L3 Craft BK

Effects such as delays can be constituent parts of sound creation, not just post-processing

Principle L3 Craft BE

Delays shorter than ~25-35 ms are heard as timbre or doubling, not as distinct echoes

Concept L1 Foundations BD

Supporting — enrichment, not gating

A phaser with feedback adds sweeping notches and a resonant peak that animate a static chord

Concept L2 First instrument B

Fractional delay times require interpolation, which trades tuning accuracy for frequency-dependent attenuation

Principle L4 Performance B

Fixed-length variable-step delay lines keep decay time constant across pitch, unlike variable-length lines

Principle L4 Performance BE

Surge XT's Ensemble effect models BBD bucket-brigade delay lines for authentic analog chorus character

Concept L3 Craft BD

Ableton's Echo is the closest built-in device to a hardware dub delay; slight L/R timing error adds character

Fact L3 Craft BDN

Distortion plus a high-feedback delay turns a dry vocal chant into an EBM industrial texture

Procedure L3 Craft BD

A noise oscillator layer gives delays textural material to sustain between note events

Concept L3 Craft BD

DelayL creates a one-shot delay; CombL adds feedback to produce echoes with controllable decay time

Concept L2 First instrument B

Delay and comb UGens allocate memory dynamically; increase s.options.memSize to avoid allocation failures

Procedure L2 First instrument BF

Surge XT's comb filter delays the signal by a pitch-tuned amount to create resonant coloration and physical-model waveguides

Concept L3 Craft B

The dry/wet balance parameter controls the mix ratio between an unprocessed and a processed signal

Concept L1 Foundations BD

All-pass filters provide delay without altering the spectrum but with frequency-dependent phase response

Concept L4 Performance BE

The dub delay throw feeds a stab into a long filtered feedback delay whose repeats degrade and darken

Concept L2 First instrument BA

Part of curricula

Electronic Music Producer — from raw sound to a released track — Write and arrange a full track recommended
Synthesist / Sound Designer — deep DSP to a performed live synth rig — The synthesis palette — FM, additive, wavetable, granular, drums required

Unlocks — modules that require this one