Reverb

Clap your hands in a bathroom, a living room and a large church, and you hear three different tails of sound after each clap. That tail is reverberation: the sound bouncing off walls, floor and ceiling and reaching your ears from every direction as it fades. Recordings made close to a microphone capture very little of it, so producers add reverb to place sounds in a believable space.

What you hear in a reverb

• Direct sound: the sound that arrives straight from the source.
• Early reflections: the first few distinct reflections from nearby surfaces, which tell the ear the size and shape of the room.
• The tail (decay): a dense wash of reflections fading away.

Common settings

• Decay time: how long the tail lasts. Small rooms have short decays, large halls and churches long ones. Acousticians measure it as the time the sound takes to fall by 60 decibels.
• Pre-delay: a short gap between the direct sound and the start of the reverb. A little pre-delay keeps a vocal clear and in front while still sounding spacious.
• Size, damping and tone: how large the space feels and how quickly its high frequencies die away.
• Mix (wet/dry): how much reverb you hear compared with the original sound.

Types of reverb

• Room, chamber and hall: imitations of real spaces, from small and close to large and grand.
• Plate: originally a large suspended metal sheet set vibrating by the sound; bright and smooth, and popular on vocals and drums.
• Spring: springs inside many guitar amplifiers, with a distinctive twang.
• Convolution: uses a recording of how a real space responds to a short sound (an impulse response), so the effect sounds like that place.
• Algorithmic: calculated by software, and highly adjustable.

Using reverb in a mix

1. Use a send. Put one or two reverbs on auxiliary tracks and send several instruments to them, so they share a space and the mix stays coherent.
2. More reverb pushes a sound back; less brings it forward. Keep the lead vocal and the main parts drier, and let supporting parts sit further back.
3. Filter the lows. Removing low frequencies from the reverb keeps the mix from getting muddy (EQ).
4. Fit the tempo. Choose decay times that clear before the next important note, or that breathe with the music.
5. Judge it in the full mix. Reverb that sounds lovely on its own is often too much with everything playing.

Pianists know a little of this effect from the sustain pedal, which lets the strings ring and resonate together (resonance).