Reverberation (reverb) is a naturally occurring phenomenon that tells our brains about the space we are in. Sound reflects off surrounding surfaces (early reflections); these reflections again reflect off all the surfaces (reverb tail) creating a ‘wash’ of echoes that remain audible briefly once the direct sound has gone. Unless the space is very large, we don’t hear reflections as distinct echoes – we simply perceive a sense of space. In close mic recordings, we normally want to minimise the reverb as once recorded, we can’t change it.

Reverb parameters

• The more reflective the room, the longer the reverb time or RT₆₀ (the amount of time taken for the reverb to fully decay so we can’t hear it any more); the pre-delay is the gap between the sound and the onset of the early reflections and reverb tail; a larger room will have a longer pre-delay – if smaller it will have a shorter pre-delay
• On a reverb unit, the pre-delay parameter us to change the room size without altering the reverb time.

Types of reverb

• Natural / room / hall reverb: musician performs in a ‘live room’ with an appropriate reverb character
• Chamber reverb – the track is played back on speakers in a reverberant space and an omni mic / stereo pair is used to capture the reverb at the opposite end which is blended with the original signal afterwards.
• Plate reverb – a mechanical reverb introduced in the 1950s along with spring reverb. It feeds an audio signal through a thin metal plate suspended in a frame where a drive transducer makes the metal sheet vibrate; these vibrations are captured by pickup transducers. Sounds bright and metallic with accentuated early reflections.
• Spring reverb – a cheaper, more practical but less sonically desirable alternative to plates; it operates on the same principle but replaces the plate with a loose spring. Mid-heavy, twangy and less rich than plate.
• Digital reverb – first seen in effect units made by EMT, Yamaha and Lexicon in the 80s, digital reverbs crate reverb through lots of mathematically calculated layered delays. Digital reverb units had presets on them.
• Reverb plugins – use digital / convolution technology (from 90s, more powerful in 00s); it is common to see plugins that emulate hardware units. It is easy to automate parameters of a reverb plugin on a DAW.
• Convolution reverb – reproduces a real reverb. An impulse is generated in a space (using e.g. white noise / sine wave sweep), and the response recorded; this gives us information about how the room responds to a signal; mathematical algorithms then subtract the impulse from the reverb and allow its application to other sounds.

Creative reverb

• Gated reverb applies a long reverb to a drum / vocal, followed by a gate, giving a dense, powerful 80s sound
• Non-linear refers to digital reverb presets that didn’t obey the laws of physics (e.g. the tail got louder)
• Reverse reverb plays the reverb tail backwards; plugins do this – in the 60s the tape direction would be reversed

Acoustics

• Surfaces reflect (as above), absorb (don’t reflect all sound waves / take in some energy) and diffuse (scatter sound waves over a large area) sounds; acoustic treatment / bass traps control this (foam panels stuck to walls)
• Standing waves are sometimes called ‘room modes’ and can cause cancellation or overemphasis of frequencies
• Flutter echoes occur between hard parallel walls where the sound repeatedly bounces back and forth.
• Comb filtering occurs when a slightly delayed version of a signal combines with the direct sound, causing destructive interference; the resulting signal sounds thinner where some frequencies cancel / reduce in volume
• Isolation booths prevent spill in both directions – from the performer and from other performers
• Monitoring on headphones is often not a good solution; no signal from the left will reach the right ear and vice versa, unlike speakers – however they are crucial when recording to avoid spill from the tracks or click
• Open back headphones sound natural as they let a bit of the background sound through but cause more spill; closed back headphones avoid spill and show up more detail but isolate you from the room more
• Translation issues occur if a setup accentuates HFs / LFs and you overcompensate, causing problems elsewhere
• Studio monitors normally have two separate drivers; the tweeter handles HFs (2kHz – 20kHz) and the woofer everything else below this; you sometimes see sub-woofers, which handle very low frequencies (<100Hz).

The impact of reverb

• Gives ambience, depth, colour and space and puts sound in a ‘place’ / recreates the sound of a room
• Brings a mix together / mix glue; reverb can give the impression that musicians are playing in a natural acoustic
• Wall of sound – 60s production technique characterised by a dense, layered sound and a big reverb applied to the whole mix; sometimes the reverb was so big that the instruments had little clarity.

Checklist

Core FX parameters

Wet, dry, mix and bypass

Types of reverb

Acoustic: room / hall reverb, chamber reverb

Mechanical: plate and spring reverb

Digital and convolution reverb

Creative uses of reverb

Gated reverb

Reverse reverb

Reverb parameters

Reverb time / RT60

Pre-delay time

High frequency damping

Describing a reverb tail

Graph of reverb tail

Describing a reverb tail; pre-delay time; early and late reflections; reverb time

How live room acoustics affect a recording

Room size, absorption, reflection, diffusion

Resonant frequencies

Acoustics parameters

Isolation booths for vocals, drums and amps

Monitor speaker

The different frequency ranges handled by tweeters, woofers and sub-woofers

Translation: checking mixes on different monitoring systems e.g. headphones, speakers, sub-woofers

Capture of sound

Avoiding interference

Development of music technology

The wider impact of reverb on the music industry