Sixty Thousand Divided by the Tempo, and Everything Else Is a Fraction

The dotted eighth is the interesting one

A delay set to a plain eighth repeats on the beat and reinforces what was played. A delay set to a dotted eighth — 375 ms at this tempo — lands between the eighths, so a simple repeated figure comes back as a pattern with more notes in it than were played, and the repeats fall on the gaps rather than on the hits. That is the effect behind a great deal of arena-sized guitar from the eighties onwards, and the reason the setting has its own name in most pedal manuals. It only works while the tempo holds: a piece that speeds up leaves the repeats behind, and the pattern turns into mud within a few bars.

Perfectly synced is not always what is wanted

The calculation gives the value that sits exactly on the grid, and a repeat that sits exactly on the grid disappears into what is already there. Nudging a delay a few milliseconds late leaves the repeat audible as a separate event, which is often the point; nudging it early makes a part feel urgent. The same applies to reverb pre-delay and to any doubled part. Use the computed figure as the centre of a small range to try rather than as the answer, and remember that a live recording has no single tempo to sync to at all — there the delay has to be set by ear against the passage it will accompany.

Frequently asked questions

Where does the sixty thousand come from?

Sixty seconds in a minute times a thousand milliseconds in a second. If you would rather work in seconds, divide sixty by the tempo instead — 60 ÷ 120 = 0.5 second per beat, the same answer in different clothes. The constant only exists because delay units are marked in milliseconds; a sequencer that thinks in ticks per quarter note does the same arithmetic against a different denominator and never shows the number at all.

Does the time signature change the answer?

Not the beat length, which depends only on the tempo, but it changes which note value the beat refers to. In a signature with a lower number of eight, the beat is conventionally counted in dotted quarters rather than quarters, so a metronome mark of 120 may mean something different from what this calculation assumes. Check what the tempo marking is attached to — a note symbol usually sits next to the number for exactly this reason — and if it is not a quarter note, convert before dividing.