tempocalculator

Reverb Calculator: Pre-Delay and Decay From BPM

At 120 BPM a 1/32-note pre-delay is 62.5 ms, and a tail that ends on the next beat needs a decay of 437.5 ms. Enter a tempo and the reverb calculator lists three pre-delay options and four decay times, from a quarter note to two 4/4 bars. Each decay subtracts the pre-delay, so pre-delay plus decay lands exactly on the grid.

Any tempo from 20 to 300 BPM, to two decimal places.

At 120 BPM a 1/32-note pre-delay is 62.5 ms. For a tail that ends on the next beat, set decay to 437.5 ms.

Pre-delay options
Pre-delayMilliseconds
1/64 note31.25
1/32 note62.5
1/16 note125
Decay time so the tail ends on the grid (with a 1/32-note pre-delay)
Tail ends afterTotal msDecay ms
Quarter note500437.5
Half note1,000937.5
One 4/4 bar2,0001,937.5
Two 4/4 bars4,0003,937.5

decay = target note length − pre-delay

Send 120 BPM to

How does the reverb calculator time a tail?

It subtracts the pre-delay from a note length so the whole reverb ends on a beat. Pre-delay is the gap between the dry sound and the start of the reverb. Decay is how long the reverb then takes to fade. Together they make the total length of the effect.

decay = target note length − pre-delay

  • Pre-delay options are a 1/64 note, 1/32 note and 1/16 note: a quarter note divided by 16, 8 and 4.
  • Decay targets are a quarter note, half note, one 4/4 bar and two 4/4 bars.
  • Decay rows all assume the highlighted 1/32-note pre-delay.

How to use it on a mix

  1. Set the tempo

    Enter the BPM, use the steppers or slider, or tap the tempo in.

  2. Choose a pre-delay

    Read the Pre-delay options table and set the reverb's pre-delay to one of the three values.

  3. Choose where the tail ends

    In the decay table, pick Quarter note for a tight room, Half note or One 4/4 bar for a hall, Two 4/4 bars for an ambient wash.

  4. Enter the decay

    Set the reverb's decay or RT60 to the Decay ms value, then fine-tune by ear.

Worked examples: pre-delay and decay at three tempos

Faster songs need shorter tails to stay clear. All rows use a 1/32-note pre-delay.

Reverb pre-delay and decay in milliseconds
Tempo1/32 pre-delayDecay to a quarter noteDecay to a half noteDecay to one 4/4 bar
70 BPM107.147501,607.143,321.43
120 BPM62.5437.5937.51,937.5
140 BPM53.57375803.571,660.71

At 120 BPM the three pre-delay choices are 31.25 ms, 62.5 ms and 125 ms. The last one is long enough to hear as a separate slap before the room.

Why timing reverb to tempo helps a mix

A tail that ends before the next hit keeps the mix clear. When a snare reverb is still loud as the next snare lands, the two blur. Timing the decay to a note value lets the tail fill the gap and then get out of the way.

Pre-delay separates the dry sound from the reverb, so a vocal stays up front while the space sits behind it. Tempo-based pre-delays also line up with echoes from the delay time table, which keeps both effects in the same rhythm. The reasoning behind each setting is covered in the guide to reverb pre-delay and decay.

Limits of the numbers

Decay settings are not identical across reverbs. Most units define decay as RT60, the time for the tail to fall by 60 dB, but some measure to a different level, so the audible end varies. Treat the values as a starting point. The decay targets assume 4/4 bars; for other meters take the bar length from the milliseconds per note table and subtract the pre-delay yourself.

Questions

What pre-delay should I use at 120 BPM?

62.5 ms, a 1/32 note, is a common start. Use 31.25 ms for a closer sound or 125 ms to push the reverb further back.

Why subtract the pre-delay from the decay?

Because the tail starts late. A 500 ms target with a 62.5 ms pre-delay needs only 437.5 ms of decay to finish on the next beat.

Does this work for plate and spring reverbs?

Yes, for any reverb with a pre-delay and decay control. Units without pre-delay use the Total ms column as the decay.