The Decay parameter of a reverb
Decay parameter represents how long it takes the reverb to fade to where you can no longer hear it. For example, if Decay is set on 4s then it takes 4s until the reverb tail falls below a level that we could hear it. The longer the decay time is, the more it pushes a track further back in the mix; while short ones, under about a second or so, makes it sound bigger.
Timing your Reverb (pre-delay and decay time) to the track can add depth without the reverb being noticeable. Delay time is similar to decay time on a reverb. Many delay plug-ins allow you to sync to the BPM of the track which automatically determines the delay times. If this option isn’t available, you can time the delay to the track by using the following formula. 60,000 divided by the beats per minute of the track, and that equals the delay time in milliseconds for a quarter note. (you can keep dividing by 2 to get a shorter timed interval).