Recording - January 2014 - 62

Algorithmic reverb generation is the
classic approach-the reverb effect is built
up by generating digital delays, simulating
the buildup of delayed reflections in a real
space. Basic controls let the user shape the
qualities of the resultant simulation.
Modeling reverbs also create the sound
from delays, but present a different set of
controls to the user, based on physical
characteristics of the simulated space
(they require a bit more physics/acoustics
knowledge to tweak purposefully).
Convolution reverbs are actual recorded
samples of real spaces, the sound of which
is superimposed on tracks in a mix. I'll
touch more on modeling and convolution
reverbs in next month's installment-for
now I'll go over the basic controls and operation of a typical classic algorithmic reverb.
The room of your dreams
An algorithm, in geek speak, is a procedure for solving a (mathematical) problem.
In this application, it's a formula (or collection of formulas) for generating a pattern of
delayed signals to simulate the reflections in
an acoustic space. The controls in this type
of reverb plug-in allow you to dial up specific results, tailoring the algorithm(s) to the
exact response you need to simulate a specific pattern of early reflections or reverberant tail, sculpting the simulated reverb to the
needs of a particular mix.
Let's start with a list of common controls: Initial Delay, Early Reflections (various controls), Balance, Room Size,
Reverb Time (Decay), Density, Diffusion,
Tone/Filtering (various controls), etc..
Some are self-explanatory; others less so.
And some plug-ins offer different ways of
addressing the same parameters.
If provided, an Initial Delay or Predelay
control determines the delay time of the
first reflection (this sometimes affects the
timing between the following reflections as
well). In a stereo mix, having the simulated
reflections start out under the original
sounds can smear the clarity of the attacks,
while putting a bit more of a gap between
the onset of the original sound and the first
delay can enhance the attacks of the notes,
keeping the mix from getting too mushy
(ahem, yes, that's a technical term).
There's always some way to shape the
early reflections-remember, the early reflection pattern establishes the shape/character
of the simulated room. Some reverbs, like
Pro Tools' classic D-Verb, simply offer a (typical) choice of preset early reflection options:
62

RECORDING January 2014

Church, Hall, Rooms, Plate, Spring, Ambience, and Non-Linear. When presented with choices like this, it's important to know which options are most suitable for different musical styles.
For example, Church, with the long reverb tail and the echo-y quality of such a space,
would be a disaster on an uptempo rock or r&b track. Hall usually means classical concert
hall, a rectangular room with resonances that might enhance orchestral strings and brass, but
be less beneficial for, say, strumming guitars. A Room setting is usually the most useful overall, often simulating an irregularly-shaped space, which could adapt well to different musical
styles (Room might also be labeled Chamber, as above). Plate and Spring settings are selfexplanatory; Ambience often refers to a pattern of early reflections minus any later reflections,
for a drier room sound. Sometimes, an Ambience-only option might be combined with later
reflections from another reverb, for more control (see the section on drum reverb below). NonLinear is a particular effect-an artificially truncated, compressed/gated reverb, popular on
drums in the '80s (Phil Collins, anyone?) but a bit clichéd now.
Other reverb units, like Logic's built-in PlatinumVerb or Sonnox's Oxford Reverb, approach
the important early reflections differently. Here, instead of ER/room presets, the user can
shape the early reflections with parameters like room shape (rectangular box, irregular
walls, etc), width, and other adjustments (this is closer in approach to modeling reverbs).
Clearly, the same options are there, just approached from a different angle. Most algorithmic reverbs also provide a control to balance the level between the early reflections and the
later reverberant field, either as a mix control, or as separate level controls for each. This is
very useful for altering the sense of depth in a mix, independently of the reverb tail.
There's always a control for room size, which may alter several aspects of the reverb
field at once-most notably the overall spacing between reflections. Sometimes, taking
a room type that would normally be a large space in the real world and making it
much smaller, or vice versa, can result in an interesting or useful ambience-this is one
area where a little experimentation can be fruitful.

You may encounter controls labeled Diffusion and Density-these adjust the spacing of the
reflections in different ways, and can significantly alter the character of a given room. Density
controls how closely spaced the reflections in the Reverb tail are. High density means closely-spaced reflections, and is generally desirable, especially on percussive sounds like drums.
Lower density means wider spacing, for a potentially more echo-y quality. This will usually
sound grainy and harsh on material with percussive transients (unless you're looking for an
effect), but that open echo-y reverb may sound great on vocals or sustained instruments.
Diffusion also affects reflection patterns, but is about the regularity (evenness) of the
reflections rather than the rate of repeats. As with Density, high or low Diffusion settings may work better with different instruments/vocals-adjust both to taste.
In real rooms, reverberant fields lose higher frequencies first as they decay-the reverb
gets duller as it fades. This effect is simulated with a lowpass filter (or two). Sometimes
there's a single filter on the whole reverb signal, sometimes there's a filter only on the
reverb tail (leaving the early reflections alone) to make the room seem smaller or darker.
Sometimes you'll have two filters, for overall tone and decay tone control.
Finally, there's always a control for Reverb Time (sometimes labeled RT60, Decay Time, etc.).
Obviously, this sets the length of the tail. As noted above, shorter tails are often better for recorded music (especially rhythmic music); set this in conjunction with a decay-only lowpass filter, if
available, for the most flexibility in making the reverb effect sit properly in the mix.
Once you're familiar with these controls, you should have no trouble adapting to any
variations you'll encounter in modeling or convolution reverbs, which I'll touch on next
month. But now, let's start taking a look at the applications of reverb in mixing. Since
the theme of this issue is drums, I'll start with a discussion of reverb for drum recordings;
next month we'll go over vocals and overall reverb usage, along with a look at other
reverb types and a few specific products.

Recording - January 2014

Table of Contents for the Digital Edition of Recording - January 2014