Reverb Explained: Pre-Delay, Decay and When to Use It

Reverb is what a room does to a sound after the sound stops. Clap once in a bathroom and you hear the clap, then a short wash of reflections bouncing off the tile. That wash is the reverb, and every reverb plugin ever made is a simulation of it. This is reverb explained from the two controls that actually decide how it feels, pre-delay and decay, with real starting numbers you can copy. I'll use the Reverb effect in SoundCraft, our free browser DAW, as the classroom, but the concepts transfer to any reverb you'll ever touch.

What a room does to sound

Three things happen when you make a noise in a real space. First the dry sound reaches your ears directly. A few milliseconds later the first reflections arrive from the nearest walls. Then hundreds of later reflections pile up into a dense tail that fades out. Your brain reads the gap before the reflections as distance from the walls, and the length of the tail as the size of the room. Those two cues are pre-delay and decay, and once you hear them as separate things, reverb stops being a mystery knob and becomes a room you're designing.

A dry recording has none of this. A vocal tracked close to a mic in a treated room sounds like it's an inch from your face, which is great for clarity and weird for realism. Reverb puts the singer in a space. The craft is choosing a space that flatters the song without burying it.

Reverb explained: what each knob does

Open the ☰ effects rack on any SoundCraft channel and add Reverb (it's the third tile, right after the EQ and Auto-Tune). The panel draws the tail you've dialed in as a graph on the left, with the pre-delay showing up as a literal gap before the curve starts. Here's the panel fresh out of the box:

• Pre-delay (0 to 250 ms) is the silence between the dry sound and the start of the tail. More pre-delay pushes the walls further away without making the reverb longer.
• Decay (0.2 to 8 s) is how long the tail takes to die. This one knob is most of the difference between a drum booth and a cathedral. SoundCraft's reverb is convolution based, so moving Decay rebuilds the impulse response it runs on, and the tail graph redraws to match.
• Hi cut darkens the tail by rolling off everything above its frequency. Real rooms absorb highs fast, so a darker tail reads as more natural and sits further back.
• Lo cut removes low end from the tail only. The dry bass stays; the boom in the reverb goes.
• Width sets how stereo the tail is, from full stereo down to mono. The dry signal is untouched.
• Mix sets the reverb's level. One quirk worth knowing: in SoundCraft, Mix controls the wet level only, so the dry signal stays at full volume no matter where you set it. Turning Mix up makes the room louder; it never makes the singer quieter.

The knobs themselves work like hardware: drag up and down, tap the arrow keys for fine steps (hold Shift for coarse ones), and double-click any knob to snap it back to its default. That last one saves you when an experiment goes sideways.

Pre-delay keeps the vocal up front

This is the setting beginners skip and engineers reach for first. With pre-delay at zero, the tail starts the instant the vocal does, and the two smear together. The consonants lose their edge and the voice moves backwards in the mix. Add 20 to 40 ms and the dry vocal lands first, clean, with the room blooming just behind it. You get the space without losing the singer. The effect is oddly large for such a small number.

Starting points that work:

• 0 to 10 ms: tight glue for drums and short room sounds, where you want the reverb welded to the hit.
• 20 to 40 ms: vocals. SoundCraft's default of 20 ms is already in the right zone; I usually nudge it higher.
• 50 to 80 ms: big dramatic spaces. Past about 60 ms the gap starts to read as a distinct slapback echo, which can be a feature or a mess depending on the tempo.

How long should the decay be?

Match the decay to the job, not to what sounds impressive in solo. Long tails are seductive when one track is playing and fatal when thirty are. Some contexts:

• Around 0.4 s: a tight drum room. Snare and claps get thicker and more live without any audible "reverb" as such. SoundCraft's Decay knob goes down to 0.2 s for exactly this kind of work.
• 1.5 to 2.5 s: the classic vocal plate zone (the name comes from old studio units that vibrated a literal sheet of steel). Long enough to feel lush, short enough to get out of the way before the next phrase.
• 4 s and up: halls and pads. Beautiful on a sparse intro or an ambient synth, and almost always too much on anything rhythmic. The knob maxes out at 8 s if you want to disappear into the fog.

A tempo trick: if the tail is still audibly ringing when the next line starts, it's too long. Faster songs need shorter decays. Slow ballads can carry tails that would drown a 140 BPM track.

Set up a vocal plate in SoundCraft

1. Create a free account. The editors are free; the paid plans sell storage and server compute, not effects.
2. Open SoundCraft and drop in a vocal (a temporary session works fine).
3. Click the clip so its channel is focused, then open the ☰ rack and click Reverb.
4. Set Decay to about 2 s, Pre-delay to 40 ms, Lo cut up to 200 Hz, Mix down to 20%.

Each move has a reason. The 2 s decay is squarely in plate territory, rich but not cavernous. Pre-delay at 40 ms doubles the default so the consonants land dry before the wash arrives. The low cut at 200 Hz strips the tail's low mids, which is energy that adds mud and zero sense of space. And 20% mix is quieter than you think you want, which is usually correct. If you're starting from a raw take, our guide to recording vocals in the browser gets you to this step, and the Auto-Tune walkthrough covers tuning, which should happen before the reverb goes on.

Why vocals drown in reverb (and the fix)

The classic beginner mix has a gorgeous vocal completely underwater. It happens because reverb adds energy everywhere the vocal already is, so the vocal is competing with a smeared copy of itself. When you notice it, resist the urge to turn the vocal up. Fix the reverb instead, in this order:

• Mix down first. Reverb should be felt more than heard. Mute the effect, then bring it back; if you only notice it when it disappears, the level is right.
• Pre-delay up. Separating the tail from the dry signal restores clarity without removing any reverb at all.
• Cut lows out of the tail. Raising the Lo cut to 200 or 300 Hz removes the part of the reverb that was masking the vocal's warmth.
• Darken it. Pulling the Hi cut down toward 5 kHz tucks the tail behind the vocal, since our ears place darker sounds further away.

The same thinking applies across a whole mix. Different reverbs on every channel turn into sonic soup, so give the mix one or two shared spaces instead. In SoundCraft, select several channels and press Ctrl+G to group them into a bus, then put a single Reverb on the group; one tail processes the sum, and the whole mix sounds like it was performed in one place. The EQ post in this series pairs well here, because a small cut on a muddy source beats any amount of reverb surgery.

The short version: pre-delay sets how far away the walls are, decay sets how big the room is, and the mix knob should end up lower than your first instinct. Start from SoundCraft's defaults (they're a sensible medium hall at 2.2 s and 35% mix), shrink or grow the decay to fit the song, push the pre-delay up for vocals, and cut the lows out of every tail. Sign up free and practice on a real take; ten minutes of turning these knobs teaches more than any article can.