Reverb Decay and Pre-Delay
Pre-delay is the gap between the dry sound and the start of the reverb; decay is how long the tail takes to fall away. Tying decay to a note length keeps the tail from smearing into the next transient. There is no universal formula, which is why the tool gives ranges, not a single number.
Pre-delay: the gap before the space
Pre-delay is the time between the dry sound and the first audible reverb. In a real room it corresponds to how long the first reflection takes to reach you — which is why a longer pre-delay reads as a bigger space.
Its practical value in a mix is separation. With zero pre-delay the reverb starts on top of the source and blurs its transient. With 20–40 ms of pre-delay the source speaks clearly first and the space arrives behind it. This is why pre-delay is the usual fix for a vocal that has gone indistinct in a large reverb.
At 120 BPM, tying pre-delay to note values gives: a 1/64 note is 31.3 ms, a 1/32 is 62.5 ms, and a 1/16 is 125 ms.
Decay: how long the tail takes to disappear
Decay, often labelled RT60, is the time for the reverb tail to fall by 60 decibels — effectively, to silence. It is the single biggest factor in how large a space sounds.
The reason to tie it to tempo is masking. If the tail is still audible when the next transient arrives, the two overlap and the mix loses definition. Setting decay to a note length gives the tail a musical boundary to end on.
Why there is no correct formula
You will find sites offering a single equation for reverb time. Treat them with suspicion. The right decay depends on:
- Arrangement density — a sparse ballad tolerates a tail that would destroy a busy mix.
- Source material — percussive sources expose a long tail; sustained pads hide it.
- Frequency content — low-frequency energy in a tail builds up far faster than high.
- Intent — a reverb can be a room, or it can be an effect. Those want different settings.
What is calculable is how long each note division lasts at your tempo. That is why the reverb time calculator gives ranges tied to note values rather than a single number pretending to be an answer.
Starting points by reverb type
| Type | Pre-delay | Decay | Character |
|---|---|---|---|
| Room | 31.3 ms (1/64) | 250–500 ms | Short and tight. Decay usually lands between an eighth and a quarter note. |
| Plate | 62.5 ms (1/32) | 500–1000 ms | Dense and smooth. A quarter to half note decay keeps it clear of the next transient. |
| Hall | 125 ms (1/16) | 1000–2000 ms | Long and wide. Half note to full bar, though at fast tempos this masks the groove. |
Values shown at 120 BPM. Use the calculator for your own tempo.
The tempo relationship in practice
Fast tempos need shorter decays, and the reason is arithmetic. At 174 BPM a bar of 4/4 lasts only 1379 ms, so a decay of 2000 ms — a comfortable full bar at 120 BPM — would span nearly a bar and a half and smear across the groove.
This is why drum and bass tends to use short, bright reverbs and why ambient music can sustain tails of several seconds. It is not genre convention for its own sake; it follows from how much time there is between transients.
High-pass the reverb return. Low-frequency energy in a tail accumulates and muddies a mix faster than anything else. Rolling off below roughly 200–300 Hz on the return lets you use a longer decay than would otherwise be workable.
Need every value at once?
The main BPM calculator shows milliseconds, delay times, reverb ranges, hertz and bar length together, updating from a single tempo.
Use the tool
Pre-delay and decay times that sit with your tempo instead of fighting it, with the note-division maths shown for room, plate and hall reverbs.
Related tools and guides
- Reverb Time Calculator Pre-delay and decay times that sit with your tempo instead of fighting it, with the note-division maths shown for room, plate and hall reverbs. Tool
- Delay Time Calculator Tempo-synced delay times in milliseconds for every note division, including dotted and triplet values, with notes on what each one does. Tool
- BPM Calculator Tap a tempo and get every value it drives: milliseconds per beat, delay and reverb times, hertz, frames and bar length. Free, instant, no sign-up.
Last reviewed Formulas published on the methodology page Spotted an error? Tell me