About the Delay and Reverb Calculator
This tool computes two of the most common time-based settings in audio production. First, it converts a song's tempo (BPM) and a chosen note division into a delay time — in both milliseconds and Hz — so an echo, ping-pong delay, or modulation effect can lock to the beat. Second, it estimates a room's reverberation time (RT60), the time for sound to decay by 60 dB, using the Sabine equation from room volume, surface area, and an average absorption coefficient.
The tempo-synced delay formula
A quarter note at a given tempo lasts 60000 ÷ BPM milliseconds. Every other note value is a fixed multiple of that quarter note:
- Whole note ×4, half note ×2, dotted half ×3
- Quarter note ×1, dotted quarter ×1.5, quarter triplet ×2/3
- Eighth note ×0.5, dotted eighth ×0.75, eighth triplet ×1/3
- Sixteenth note ×0.25
Multiply the quarter-note length by the chosen multiplier to get the delay time in milliseconds. The equivalent rate in Hz is 1000 ÷ delay time (ms) — useful when a plugin asks for a modulation rate instead of a millisecond value.
The Sabine reverb time formula
Reverberation time is estimated with the Sabine equation, published by physicist Wallace Clement Sabine in 1898 and still the standard first-pass model in architectural acoustics:
RT60 = 0.161 × V ÷ A
where V is the room volume in cubic meters and A is the total absorption in metric sabins, calculated here as total surface area (m²) multiplied by an average absorption coefficient (α, a unitless value from 0 to 1). A higher α means more sound-absorbing surfaces — carpet, curtains, or acoustic foam — and a shorter, drier decay; a lower α (hard tile, glass, bare concrete) means a longer, more reflective decay.
Why the two numbers are compared
Mix engineers frequently check a synced delay's repeat time against the room or reverb plugin's RT60 to keep the two effects from smearing together. If the delay time is a small fraction of RT60, the echoes tend to sit inside the reverb wash rather than stand out. If the delay time is a large fraction of RT60, distinct rhythmic echoes ring out past the reverb tail. This calculator reports that ratio as a quick sanity check — it is a mixing convention, not a fixed rule, and the right balance always depends on the material and the desired effect.