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Audio Delay & Echo Time Calculator

Calculate musically-synced delay times from BPM and note value, plus acoustic propagation delay from speaker distance.

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Formula

t_beat = 60000/BPM ms, t_prop = d/c × 1000

BPM— Beats per minute (bpm)
c— Speed of sound (m/s)

How It Works

Delay time in audio has two distinct applications. (1) Rhythmic delay for musical effects: the delay time is synchronised to the tempo (BPM) of the music. A quarter-note delay at 120 BPM has t = 60000/BPM = 500 ms. Subdivisions scale this: a dotted-eighth note delay = 750 ms, a sixteenth note = 125 ms. Tempo-synced delays create rhythmic echo effects that sit 'in time' with the music. (2) Acoustic propagation delay: sound travels at approximately 343 m/s at 20°C. A speaker 10 m away has a propagation delay of t = d/c = 10/343 = 29.2 ms. In live sound reinforcement, delay loudspeakers (front fills, delays, distributed systems) must be delayed by the propagation time from the main system to their position, plus additional delay equal to the propagation time from main speakers to the delay speaker position, to ensure the delayed loudspeaker reinforces rather than confuses the main system. Delays below ~50 ms cause the Haas effect (early reflection perceived as direction); delays above ~50 ms are perceived as discrete echoes.

Worked Example

Tempo: 120 BPM. Note division: quarter note (4). Speaker distance: 10 m. Beat (quarter note) delay: t_beat = 60000 / 120 = 500 ms With quarter-note division (noteValue = 4): t_note = t_beat × (4/4) = 500 ms Eighth-note delay: t_note = 500 × (4/8) = 250 ms Sixteenth-note delay: t_note = 500 × (4/16) = 125 ms Dotted-eighth (1.5 × eighth): t_note = 375 ms Acoustic propagation delay at 10 m: t_prop = 10 / 343 × 1000 = 29.2 ms For a live PA delay speaker at 30 m from the main system: t_delay_setting = (30 m / 343 m/s) × 1000 = 87.5 ms Plus 10–20 ms additional 'leading' delay to ensure precedence to the main system.

Practical Tips

  • ✓For studio delay effects, common delay times for various note values at 120 BPM: whole note = 2000 ms, half = 1000 ms, quarter = 500 ms, dotted-quarter = 750 ms, eighth = 250 ms, dotted-eighth = 375 ms, sixteenth = 125 ms. Dotted-eighth is the classic 'U2 Edge' delay time.
  • ✓In live PA, use RTA (real-time analysis) or measurement software (Rational Acoustics Smaart, SysTune) to verify time alignment between main and delay speakers by measuring the impulse response at seats in the overlap zone.
  • ✓For multi-speaker distributed systems (halls, airports), each speaker zone must be delayed relative to the furthest upstream speaker. Calculate total delay chain as the sum of propagation times between each loudspeaker position in sequence.

Common Mistakes

  • ✗Setting delay speaker timing to match the propagation time exactly — in live sound, delay speakers are typically set 10–20 ms behind the propagation-correct time (adding extra delay). This uses the Haas effect: the audience hears the main system first and perceives its direction as the primary sound source, preventing the delay speaker from appearing to have a different location.
  • ✗Forgetting temperature correction — the speed of sound varies with temperature: c ≈ 331 + 0.6 × T (°C) m/s. At 30°C, c ≈ 349 m/s (2% faster than 20°C). For precise time-alignment in temperature-varying outdoor venues, correct the propagation delay calculation.
  • ✗Confusing millisecond delay with BPM for tap tempo effects — tap tempo pedals calculate delay time directly from the tap interval (t_ms = 60000/BPM). If the pedal has note division settings, the displayed tempo and the actual delay time are different — verify the output waveform against a clock.

Frequently Asked Questions

t = 60000 / 140 = 428.6 ms. For dotted-eighth (the most musical delay time for this genre): 428.6 × 0.75 = 321.4 ms. For sixteenth note: 428.6 / 4 = 107.1 ms.
The Haas (precedence) effect: sounds arriving within ~1–30 ms of the first sound are fused with it and perceived as one event. From ~30–50 ms, a 'colouration' or 'spatial' effect is heard. Above ~50 ms, a discrete echo is perceived, separate from the original sound. In reverberant spaces, this threshold can be lower.
Propagation delay = 25 / 343 × 1000 ≈ 72.9 ms. Set the delay speaker's delay processor to this value to align it with the wavefront from the main system. Add 10–20 ms extra (total ~83–93 ms) to ensure the main PA takes precedence in the overlap zone between main and delay speakers.

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