Recording - January 2014 - 60

Part 1

By Joe Albano
Reverberation-it's all around us whenever we hear
music in an enclosed space, but most listeners rarely
give it much thought, until they begin recording and
mixing music. Then reverberation (reverb, for short)
becomes a very important aspect of any recording or
mix-getting it right can mean the difference between
a rich sound with lots of depth and clarity, or a mix
that's either overly dry and dead, or muddy and lacking detail and dimension.
This 2-part article will study reverb in recording and
mixing-from capturing the real thing to creating richsounding simulations with the best of today's technology-and some approaches to applying reverb to
enhance any recording.
The nuts and bolts of reverb
So what is reverb? We think of it as the sound of a
room-the collected reflections of sound waves in a
room, all blending together to form a sound field that
will (hopefully) enhance the music played there. But to
an acoustician or professional engineer, the term has a
specific technical meaning.
The reflections that make up a room's reverb are in three
parts. First there's the initial reflection, the first echo to
reach the listener. This provides a subconscious indicator
of room size-the longer the delay before that first echo
(sometimes called predelay), the larger the room. Then
there are early reflections (sometimes called ambience), a
buildup of of relatively distinct reflections that define the
shape and character of the room-a rectangular box, a
space with curved walls or irregular surfaces, etc.. And
finally there are the late reflections or reverb tail, a denser
buildup of late reflections that may tail off well after the
original sound stops. The character of the tail is determined by the liveliness of the room-reflective surfaces like
wood or concrete vs. absorbent materials like carpet,
foam, or an audience-as well as room size.
The length of the tail is called the reverberation time
(also called decay, decay time, or simply "time"). It's
often written as RT60, the time it takes for a sound to
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RECORDING January 2014

decay by 60 dB from initial level. Typical reverbs
default to 3-4 seconds of RT60, which is way too long
for most applications; Carnegie Hall's RT60 is only 1.8
seconds! Typically, rhythmic pop music will do fine with
RT60 set to one second or less.
When we talk about reverb in general, we mean all
three parts together, but when adjusting a reverb
device, we need to remember the individual components as we adjust our sound.

Capturing the room
In the most basic recordings, like those made with just
a stereo pair of mics, the only reverb involved is that of
the actual space, and the trick is to position the mics to
capture the right amount. Too close to the direct sound
source (the instruments/voices) may result in a recording that's too dry (lacking in reverberant richness); too
far away may allow the reverb to dominate, for a sound
that's muddy and lacking in necessary detail.
Remember that in a real space, reverb is all around
the listener; our ears and brain can tolerate a lot of room
sound before we lose clarity, because we favor sound
from the front (the stage). But when you play back a
recording over speakers, everything comes at you from
the front, including all the reverb, so a space that sounds
fine in person might sound too muddy on playback.

Recording - January 2014

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