BPM → Delay & Reverb Time (ms)

One number, then everything else

At a given tempo a quarter note lasts 60,000 ÷ BPM milliseconds — at 120 BPM that is 500 ms — and every other division follows by halving or dotting. Getting that one figure right gives you delay times, LFO rates, reverb pre-delay and gate timings without further arithmetic.

The time signature setting matters for how the divisions are grouped rather than for the underlying millisecond value; a beat is a beat, but what counts as a bar is not.

Dotted and triplet values, and why delays use them

A dotted eighth is the workhorse of rhythmic delay because it sits deliberately off the beat — at 1.5× an eighth, repeats fall between the main pulses and create the syncopated pattern associated with a great deal of guitar and electronic music. A straight eighth delay reinforces the beat instead, which is sometimes what you want and often sounds like a doubling rather than an effect.

Triplets divide the beat in three and produce a rolling feel against a straight rhythm section.

Precision matters more than it seems: a delay a few milliseconds out drifts audibly across a bar, and the drift compounds with each repeat. This is exactly the case where a calculated value beats a knob set by ear.