Specifications

An Introduction to Reverberation
The
ZOOM 9 120 sound environment processor specializes in digital simulations of acoustic spaces,
but
also extends that capability with powerful parameter controls.
Acoustic simulations using
Reverberation is the acoustic phenomenon which occurs
when sound waves are reflected off surfaces such as the
walls, floors and ceilings of an enclosed space. Since
sound emits from a source in many directions, and
encounters multiple surfaces at various distances and
angles, these
can be many reflections of a single instant,
each repeating at slightly or greatly different times and
levels, until they lose energy. These reflected waves
make a sonic "residue" which reinforces the source by
repeating
in tiny echoes every moment of sound.
Even when the source has stopped generating the sound,
reverberation will continue to decay for some time-the
period depends on the size of the enclosure and the
materials of which it is made. The 9120 calls this period
of decay
reverb time (RevT). The reverb times of
average-sized, medium-surfaced rooms are usually short
(0.3 - 1.4 seconds), concert halls and opera houses
somewhat longer
(1.8 - 3.0s), and large empty halls and
churches very long (3.4
- 7.0s).
The ZOOM 9 120 exceeds the focus of acoustic space
modeling by extending parameter controls beyond values
necessary to simulate those spaces. So, for example,
reverb time range extends to a full 10.0 seconds,
allowing you
to create unusually spacious environments.
Reverb, then, is no more
than a series of multiple echoes,
enhancing sustained sounds with repetitious support, and
at the same time smearing sudden changes
in volume like
the transient attacks of a percussion instruments. Most
often, reverberation simply provides an ambient
environment which we take for granted. There is such a
density of reflections in an enclosed space, at so very
many different levels and times, that
the resulting
acoustic effect is smooth and natural-so natural, in fact,
that the effect in a small or medium-sized room is most
often completely unnoticeable. For example, the ambient
reverberations resulting from a conversation in a typical
living room would not be perceived unless the room were
to become instantly sound-proofed, upon which the void
of natural ambience would then become uncomfortably
obvious.
Or perhaps, because of particular shapes and
surfaces (often found in cheaply constructed meeting
rooms or apartment building hallways), a space has a
strong resonant reverberation at a particular frequency
(known as "standing waves") which can become
annoyingly obvious. The reverb algorithms
in the 9120
are designed to
be completely free of such resonances.
In standing very close to a person in conversation, you
definitely hear the direct sound of their voice well before
the first of the many reflections. But the further you are
from the source, the less this is true, until the distance is
large enough that you might
be receiving all of them at
the same time.
The same is true in a concert hall. The
people in the first row receive the direct sound from the
stage before most of the reverberations, whereas those
toward the rear of the hall hear a more equal mixture.
Digital
reverb devices can easily delay the beginning of
the reverb effect by a specific amount. This control in
the 9120 is called pre-delay time (PreD). In addition to
simulating acoustic ambience, pre-delay is useful for
allowing the complete attack dynamics of an instrument
to sound in a music mix before becoming smoothed with
reverb.
Reflected sound waves will lose their energy eventually
no matter what the environment. In spaces with hard
reflective surfaces, such as glass or tiled rooms, this
process takes a long time because these surfaces reflect
the energy efficiently so that the waves lose relatively
little each time they bounce off. Conversely, softer
materials, covered with carpet or heavy drapes, absorb
the sounds quicker.
In this case, higher frequencies lose
their energy faster than long, low
waves. In this way, the
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Section III : Effects and and Their Parameters
9