How to use
Enter a tempo in beats per minute, where one beat is a quarter note. Choose a note value and rhythm for pre-delay, then independently choose them for decay. Calculate to get a pair of millisecond values and their combined duration. The defaults provide a short pre-delay and a longer decay as an editable starting point, not an acoustic recommendation.
Pre-delay is the interval before the reverb begins. Here decay is a separate duration that begins after that interval. The total is their sum, not a decay value from which pre-delay has already been subtracted. Copy the pair into your session notes and use your ears when applying it in a processor.
The pale examples calculate without editing. Focusing any numeric field clears all examples together; later edits keep your own values.
The formula
A quarter-note beat lasts 60,000 / BPM milliseconds. For a selected note 1/n, multiply that beat by 4/n. Straight rhythm uses factor 1, dotted uses 1.5 and triplet uses 2/3. Each selected note is calculated independently with its own rhythm factor.
The supported notes run from a whole note (1/1) to a sixty-fourth note (1/64). A triplet note lasts two thirds of the corresponding straight note, while a dotted note adds half its length. This calculator assumes a steady tempo; it does not follow tempo automation or interpret a time signature.
Two examples
At 120 BPM, a quarter note is 500 ms. A straight 1/64 pre-delay is 31.25 ms and a straight 1/2 decay is 1000 ms. Their combined span is 1031.25 ms.
At 90 BPM, a straight quarter note is about 666.67 ms. A triplet 1/16 pre-delay is about 111.11 ms and a dotted 1/4 decay is 1000 ms. The total is about 1111.11 ms. Calculations use unrounded values before displaying two decimals.
Inputs and output
BPM must be greater than zero and no more than 1000. A decimal point or comma is accepted without grouping. Missing, zero, negative and non-finite tempo values produce an error. Extremely small values that overflow calculation are rejected.
Copy result includes pre-delay, decay, total, quarter-note length and the selected formula factors. Editing a number or selection removes the previous result and copy state. Clear empties the tempo while preserving note and rhythm choices. Calculate again after editing.
Is this the room’s reverberation time?
No. It does not calculate or measure room RT60, absorption, room dimensions or equipment response. These are musical timing references derived from tempo.
Will matching the beat make the best reverb?
Not necessarily. Arrangement, source material and the processor’s decay behavior all matter. Tempo alignment alone does not predict sound quality.
Should I subtract pre-delay from decay?
Not for the pair shown here: decay starts after pre-delay. If your workflow requires a fixed combined endpoint, choose the pair accordingly rather than treating the displayed total as decay.
Can I hear or synchronize the result?
This tool outputs text only. It does not play audio, detect BPM, connect to a DAW or control a plug-in.