Reverb

Clap once in an empty stairwell and you hear reverb: thousands of reflections off the walls arrive so close together that they blur into one fading tail. When the reflections come back far enough apart to hear one by one, you have an echo, which is what a delay effect makes.

A reverb effect usually has four controls:

• Type or size: a small room, a concert hall, a plate (an old studio trick, a large steel sheet set vibrating, bright and smooth) or a spring (the drippy sound built into many guitar amps).
• Decay, or reverb time: how long the tail lasts. Under a second sounds like a room, around 2 seconds like a concert hall, and 5 seconds or more like a big stone church.
• Pre-delay: a short gap before the reverb starts. 20 to 40 ms lets the start of each note through clean.
• Mix (also amount, or wet and dry): how much reverb you hear against the original sound.

Turning up the mix pushes a sound further back, as if you stepped away from it. A longer decay makes the space bigger but blurs fast notes into each other. Slow pads and chords can take a 2 to 3 second tail at 20 to 30 percent mix. Bass and kick drums usually stay nearly dry, or the low end turns to mud. To hear the difference, play an A minor chord (A, C, E) with no reverb, then with a 3-second hall at 30 percent mix, and the chord moves from right in front of you to the far end of a big room.

In Gelato Synth, the Space page has Reverb, Size and Decay sliders next to the two echo sliders, and Gelato Chord has reverb among its FX. Making a synth sound bigger shows where reverb fits with detune and chorus, and dreamy chord progressions are a good place to hear what a long tail does.