Why does the suggested decay change with the tempo?

Because a tail has to fit between beats to avoid smearing the music. At a slow tempo a beat is long, so a generous decay still clears before the next one; at a fast tempo the same decay would still be sounding when the next note arrives, which reads as blur rather than space.

Why does the plate ignore room size?

Because a plate is a sheet of metal with transducers on it rather than a room, so its density comes from the material and not from distance. That is why its figures are a short pre-delay and a decay based on the beat with a floor, rather than the scaling the three rooms use.

The time it takes for a reverb tail to fall by sixty decibels, which is the point at which it is effectively inaudible. It is the standard way to state a decay time, so a figure in that column can be typed straight into any reverb that asks for a decay or RT60 value.

Is the pre-delay really about keeping consonants sharp?

That is its main use on vocals. Holding the tail back by ten to thirty milliseconds lets the dry attack register before the reflections arrive, so the words stay clear even when the space behind them is large. A plate's near-zero pre-delay is the deliberate opposite, trading separation for density.

Should I use these figures as they are?

Use them as starting points. They are derived from the tempo and a rough room character, and they say nothing about how wet the mix should be or how the reverb sounds. Setting them and then listening is faster than guessing from nothing and then adjusting.

Reverb Time Calculator

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Reverb Time Calculator suggests a pre-delay and decay for a tempo and a room character, so a reverb's tail sits with the music instead of blurring across it. The figures are a mixing starting point, not a rule.

What is Reverb Time Calculator?

Enter a tempo, choose a room character, and the panel gives a pre-delay and a decay in milliseconds, along with the length of one beat at that tempo.

The inputs and the two figures:

A tempo from one to four hundred beats per minute, defaulting to a hundred and twenty.
Four room characters: a small room described as tight and transient-safe, a medium room for general vocals, a large hall for ballads and pads, and a plate described as dense with a short pre-delay.
A pre-delay figure and a decay figure, each in milliseconds, in their own panel.
A note giving the beat length at the chosen tempo and explaining that the suggested decay keeps reflections from smearing across the next beat.

Both figures are derived from one measurement, the length of a beat, and a room-dependent multiplier. A small room suggests ten milliseconds of pre-delay and half a beat of decay, a medium room twenty milliseconds and a full beat, and a large hall thirty milliseconds and a beat and a half. The plate is the exception, and deliberately so: it uses eight milliseconds of pre-delay and a decay of a beat and a quarter with a floor of eight hundred milliseconds, because a plate's density comes from the metal rather than from distance and the usual advice about room size does not apply to it. The reason the decay is expressed as a fraction of the beat is that a tail that outlives the next beat makes the music sound smeared rather than spacious, so a busier tempo wants a shorter decay for the same room. Pre-delay does something different: it holds the onset of the tail back from the dry sound, which is what keeps a vocal's consonants sharp while a large sounding space sits behind it. Ten to thirty milliseconds is the usual range for that separation, and a plate's near-zero figure is a feature of the design rather than an oversight. The decay figure is labelled as RT60, the time for the tail to fall sixty decibels, which is the standard way reverb length is described.

What the figures do not decide:

How much reverb to use, which is the wet and dry balance.
The tone or colour of the tail, which is set by the reverb's own controls.
Anything about the frequency response of the room being imitated.
Diffusion, density or modulation settings inside a specific plugin.
The effect of other processing, such as a compressor that lifts the tail.
Nothing is measured from audio; the figures come from the tempo you enter.

Use it before dialling in a reverb: choose a room, take the suggested pre-delay and decay as your starting values, then listen and adjust. When the effect to be timed is a delay rather than a tail, the delay time calculator gives note-division times instead, and when the reverb itself is the thing being produced rather than configured, the reverb simulator and the convolution reverb render it as audio.

How to use Reverb Time Calculator

Enter the tempo of the material being mixed.
Choose the room character closest to the space the mix should suggest.
Read the suggested pre-delay and decay in milliseconds.
Set those values in the reverb and adjust by ear from there.

When to use Reverb Time Calculator vs related tools

Reverb Time Calculator is the tool for choosing a starting pre-delay and decay that will not fight the tempo. Delay Time Calculator answers the equivalent question for echoes and modulation rates. When the goal is to hear a reverb rather than configure one, Reverb Simulator and Convolution Reverb render the audio, and BPM Calculator supplies the tempo if it is not known.

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