Pre-delay is the time between the direct sound and the start of the reverb’s first reflections or tail. It is often set from a few milliseconds to a few tens of milliseconds, creating a small gap between the source and the reverb. It is not the length of the tail itself, but it strongly changes the sense of front-to-back placement and the clarity of words.
The gap between source and tail
With a short pre-delay, the source and the reflections overlap immediately, tending to sound like a close space or a fused ambience. A longer setting lets you hear the attack of the source before the tail continues, so the outline stays intact. Too long, and it can start to sound like a separate delay.
Relationship to distance
Pre-delay is not a knob that directly sets room size, but it does affect the impression of space. On vocals or snares you want up front, a slightly longer setting separates them from the tail. Short values suit material you want to blend into the space.
Matching the tempo
One approach is to set a time close to the beat or one of its subdivisions at the song’s tempo. Syncing is not always the right answer, though. Listen to the lyrics and the speed of the attacks, and find a position where the source stays clear and the tail does not fight the rhythm.
How to dial it in
First set the reverb amount and the decay to establish a rough space. Then raise the pre-delay from a short value and find the point where the source steps forward. To make the change easier to judge, keep the dry/wet or send amount steady and compare within the song.
A common mix-up
Pre-delay is a different setting from a delay that creates repeats. It only postpones the start of the reverb. The basics of balancing source and ambience are covered in the reverb article.
