This delay and reverb time calculator converts a tempo into effect settings. Not the tempo itself, and not a table of note lengths — the specific millisecond values you type into a reverb: how long to hold the sound back before the tail starts, how long the tail should ring, and how the delay line underneath it should be spaced so the two effects agree with the groove rather than fight it.
Arb Digital maintains a free tools library that covers audio, video and production maths alongside the marketing calculators the agency is better known for, because a lot of the work that lands on a marketing team's desk is a podcast edit or a video voice-over. If you already know your tempo, the BPM calculator is the page that finds it and lists every note length in milliseconds. This page picks up from there and turns those lengths into reverb and delay parameters, which is a different question with different answers.
What This Delay and Reverb Time Calculator Does
Enter the tempo, choose how long you want the reverb tail to last in beats, pick a pre-delay note value and a delay division, and the calculator returns four working numbers. The headline figure is the reverb decay time in milliseconds and seconds. The supporting grid gives the pre-delay in milliseconds, the delay time for your chosen division, the total tail — pre-delay plus decay, which is the number that actually determines when the reverb has finished — and how many delay repeats will remain audible before they fall below the noise floor.
Underneath the headline the tool shows the straight, dotted and triplet variants of the division you selected, because those three are what you will end up auditioning against each other. The bar display puts pre-delay, decay, delay and one full bar on the same scale so you can see at a glance whether the tail fits inside the bar or spills over into the next one.
Here is the boundary with the closest tool already on the site. The BPM calculator finds the tempo by tap or beat count and lists note lengths in milliseconds, samples and hertz. It does not know about pre-delay, decay time, tail length or feedback, because those are not properties of a tempo — they are choices you make about an effect. This page owns those choices. If you want the tempo, start there; if you have the tempo and need reverb settings, stay here.
How to Use It
- Enter the tempo. Take it from your project's transport, or find it with the BPM calculator if you are working with an imported file.
- Set the beats per bar. This only affects the bar-length reference at the bottom of the display, but that reference is how you judge whether a tail is too long.
- Choose a tail length in beats. Two beats is a sensible starting point for most modern productions. Half a beat is a tight ambience; two bars is a wash.
- Pick a pre-delay note value. A 1/32 note keeps the reverb close; a 1/16 or 1/8 note opens a clear gap that protects the front of a vocal.
- Set the delay division and feedback. The dotted eighth is the default here because it is the most useful rhythmic delay in popular music, for reasons covered further down.
The Formula / How It's Calculated
Every number on this page comes from one conversion. A beat, meaning a quarter note, lasts 60,000 divided by the tempo milliseconds. At 120 BPM that is 500 milliseconds. Everything else is a multiple of that beat.
Reverb decay is the tail length in beats multiplied by the beat. Two beats at 120 BPM is 1,000 milliseconds, so you would set the decay control to 1.0 second. Pre-delay is the chosen note value expressed as a fraction of a beat, multiplied by the beat: a 1/32 note is one eighth of a quarter note, so 0.125 times 500 gives 62.5 milliseconds. Delay time is the same operation with a different factor — a dotted eighth is 0.75 of a beat, so 0.75 times 500 gives 375 milliseconds.
The repeat count is the one figure that is not a simple multiplication. Each repeat of a delay is quieter than the last by a fixed ratio set by the feedback control, so the decibel drop per repeat is 20 × log₁₀(feedback). At 40 per cent feedback that is a fall of about 7.96 dB per repeat, and reaching the conventional 60 dB decay floor therefore takes 60 ÷ 7.96, or roughly 7.5 repeats. The tool reports 7, because the eighth repeat has already dropped below the point where you would hear it in a mix.
Worked example, all four numbers at once. Tempo 120 BPM, tail 2 beats, pre-delay 1/32, delay dotted eighth, feedback 40 per cent. Beat = 500 ms. Decay = 1,000 ms. Pre-delay = 62.5 ms. Delay = 375 ms. Total tail = 62.5 + 1,000 = 1,062.5 ms, which is longer than a bar of 4/4 at that tempo (2,000 ms) will comfortably hide behind a busy arrangement but comfortably shorter than the bar itself.
Pre-Delay Is the Control That Actually Buys You Clarity
Most people reach for a shorter decay when a reverb is smothering a vocal. The better first move is usually a longer pre-delay. Pre-delay is the gap between the dry signal and the onset of the reverb tail, and while that gap is open the listener hears the source completely unmasked. Consonants, transients and the front edge of every word land in clear air.
The reason it works is a well-documented feature of hearing: a reflection arriving within a few tens of milliseconds of the direct sound is fused with it rather than heard as a separate event, and the perceived position stays with the first arrival. Push the gap wider and the reverb starts to read as a distinct space around the source rather than a haze on top of it. That is why a 60 to 80 millisecond pre-delay so often rescues a lead vocal that a shorter decay could not.
Tying pre-delay to a note value rather than picking a round number has a second benefit. When the gap is a musical subdivision, the reverb onset lands on a grid position rather than in between, and the whole effect reads as part of the arrangement. At slower tempos a 1/32 note is a long gap and at fast tempos it is very short, which is exactly the scaling you want — a ballad can carry a wide pre-delay that would smear a drum-and-bass track.
Why the Dotted Eighth Is the Default Delay
A dotted eighth is three sixteenth notes long, which means its repeats do not land on the same grid positions as the main eighth-note pulse. Instead they fall between the hits, and after three repeats the pattern lines up with the beat again. The result is a delay that adds rhythmic movement without doubling anything already in the arrangement, which is why it is the default setting on so many guitar and synth patches and why it turns up on an enormous number of records.
Contrast that with a straight eighth-note delay, which places every repeat exactly on an existing subdivision. If the part is already playing eighths, the delay simply thickens what is there and the mix gets denser without getting more interesting. A triplet delay creates a cross-rhythm against straight material and is powerful but far more intrusive, so it usually wants a lower feedback setting and a lower level in the mix.
Matching Decay to Tempo Without Making Mud
A reverb tail that is still audible when the next accent arrives blurs the boundary between the two, and the mix reads as smeared rather than spacious. The fix is to treat the total tail — pre-delay plus decay — as a time budget against the length of one bar, which is what the bar display on this page is for.
At 120 BPM in 4/4, a bar is 2,000 milliseconds. A total tail of 1,062 milliseconds occupies just over half of it, which leaves clear air before the next downbeat. Take the same settings to 160 BPM and the bar shrinks to 1,500 milliseconds while a two-beat tail shrinks to 750, so the proportion holds. That is the advantage of specifying a tail in beats rather than seconds: it scales with the song automatically. Specify 1.2 seconds of decay and it will be perfect at one tempo and wrong at every other.
Where the rule breaks down is with sparse arrangements. A solo piano piece can carry a tail two or three bars long because there is nothing for it to collide with, and a dense mix at the same tempo may need the tail cut to half a beat. Treat the beat-based figure as the starting point and shorten it whenever the arrangement gets busier, not whenever the tempo changes.
Decay Time, RT60 and What the Number Means
The decay control on a reverb is calibrated in the same units as the acoustic measurement it imitates. Reverberation time is defined as the time taken for the sound pressure level to fall by 60 decibels after the source stops, which is why it is written RT60 or T60. Georgia State University's physics reference explains the underlying reverberation time relationship in terms of room volume and absorption, and its companion page on reverberation and its perceptual effects covers why the same tail sounds different on speech and on music.
The consequence for mixing is that a decay setting of 1.5 seconds does not mean the reverb becomes inaudible after 1.5 seconds. It means it has dropped 60 decibels by then, and in a quiet passage a signal 40 decibels down is still perfectly audible. The tail you actually hear in a sparse section is longer than the number on the dial; in a loud, dense section it is shorter, because the rest of the mix has masked it. This is why a reverb that sounded right when you soloed the vocal often sounds too short in the full mix, and it is a masking problem rather than a settings problem.
Real rooms also decay unevenly across frequency. Low frequencies typically ring on longer than high ones because most absorbent surfaces work better at high frequencies, so a plugin whose damping controls are set flat can sound artificially bright. If your reverb has a high-frequency damping parameter, pulling it down usually makes a tail sit more naturally than shortening the decay does. For the frequency side of that work, the frequency converter and the wavelength calculator are the relevant pages, and the sound level converter handles the decibel arithmetic behind the 60 dB definition.
Feedback, Repeat Count and Where Delays Go Wrong
Feedback is a ratio, not a duration, and it behaves geometrically. At 50 per cent each repeat is 6 decibels down on the one before, so a delay dies away in about ten repeats. At 80 per cent the drop is under 2 decibels per repeat and the delay runs for roughly thirty, which at a dotted-eighth spacing means the tail lasts more than ten seconds. At 95 per cent it is over a hundred repeats and the effect is functionally an infinite hold.
That non-linearity catches people out constantly. Moving feedback from 30 to 40 per cent adds about two repeats. Moving it from 85 to 95 adds about eighty. If a delay is washing out a section, the fix is almost always a few percentage points off the feedback rather than a shorter delay time, because shortening the time makes the repeats faster without making them fewer.
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Content Marketing Services Talk to Arb DigitalCommon Mistakes to Avoid
- Setting decay in seconds instead of beats — a fixed 1.2 seconds is right at one tempo and wrong at every other, while a two-beat tail scales with the track automatically.
- Ignoring pre-delay when a vocal gets buried — widening the gap usually restores clarity faster than shortening the tail, and it keeps the sense of space intact.
- Forgetting that the total tail includes pre-delay — a 1,000 millisecond decay with 80 milliseconds of pre-delay finishes at 1,080, which can be the difference between fitting inside a bar and not.
- Treating feedback as linear — the last few percentage points below 100 add far more repeats than the first eighty do combined.
- Using a fixed millisecond delay on a tempo-automated project — the repeats drift out of sync, so use a host-synced delay when the tempo moves.
Related Free Tools From Arb Digital
Find the tempo first with the BPM calculator, work out pitches and note names with the note frequency converter, build harmony with the chord calculator and the music scale generator, and shift a part to another key with the music transposer. The noise exposure calculator covers the safe-listening side of long mixing sessions. Everything else sits in the free online tools hub.
Frequently Asked Questions
A BPM calculator finds the tempo and lists how long each note value lasts. This page takes a tempo you already have and turns it into reverb parameters — pre-delay, decay time and total tail — plus the matching delay time and repeat count, which are settings rather than measurements.
Somewhere between 20 and 80 milliseconds suits most vocals, and tying it to a note value keeps it proportional to the tempo. Wider gaps preserve consonant clarity because the direct sound is heard before any reverb arrives.
It means the tail has fallen 60 decibels below its starting level after one second. It does not mean the reverb is inaudible at that point, because in a quiet passage a signal well above the noise floor is still easy to hear.
A dotted eighth is three sixteenths long, so its repeats fall between the main pulse rather than on top of it and realign with the beat every three repeats. That adds rhythmic movement without thickening what is already playing.
It depends on feedback, and the relationship is geometric rather than linear. Each repeat falls by 20 times the base-ten logarithm of the feedback ratio in decibels, so 40 per cent gives about seven audible repeats and 80 per cent gives roughly thirty.
In a dense arrangement it usually should, so the tail has died away before the next downbeat. Sparse material can carry tails several bars long because there is nothing for them to collide with.
Yes. The values are plain milliseconds derived from the tempo, so they transfer to any device with numeric pre-delay, decay and delay-time controls. Units that only offer vague labelled positions will need setting by ear against these figures.
Real surfaces absorb high frequencies more than low ones, so natural tails lose treble as they decay. Reducing a plugin's high-frequency damping usually sounds more natural than shortening the decay time.
