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acoustics of a room that is much smaller in size.
In addition to the capability of human hearing to determine the direction from where a sound phenomenon
arrives, we can also hear modulations of acoustic events. Of importance in this context is the frequency of the
modulated signals. Frequency modulations below 100 Hz are virtually inaudible. However frequency modula-
tions can clearly be heard when occurring in the midrange frequency band, due to the "sensitivity" of human
hearing. The ear immediately detects changes in midrange frequencies, while its sensitivity to frequency
modulation in the extreme low end of the frequency spectrum is reduced. Frequency modulation can also be
used to produce wanted effects. The popular chorus effect, for instance, is basically the sum of a variety of
frequency modulations. The original signal is slightly delayed in the chorus algorithm, then added again and
modulated by means of an oscillator. Subsequently, modulating frequencies (of different pitch) are applied to
the original signal, which produces the well-known floating chorus sound. Basically, frequency modulation is
the starting point for all kinds of chorus-type effects: by simply adding the delayed signal, without modulating
the original, you can produce a delay effect. Since chorus effects use very short delay times, the resulting
delay effect is not perceived as such. However, when you increase the delay time, there is a clear gap between
original and effect signals, and delay becomes audible. A highly intensive effect can be achieved by combining
reverb/delay programs with modulation effects. For this reason, the BEHRINGER VIRTUALIZER PRO also
features multi-effects programs combining reverb or delay with, for example, a chorus effect.
In addition to the multi-effects programs and special-purpose effects, most of the VIRTUALIZER PROs effect
programs offer "pure" reverb programs, because "common" reverb is still the most important effect for mix-
down or live applications. Therefore, we at BEHRINGER want to provide you with a variety of reverb programs,
so that you have appropriate presets available for each specific application.
Before you can simulate any reverb phenomena, you need to identify the major parameters of natural reverbera-
tion and use them to create a mathematical algorithm. The BEHRINGER VIRTUALIZER PRO benefits from the
newly developed virtual acoustics algorithm. Unlike many other conventional reverb algorithms, the virtual
acoustics algorithm reproduces the essential parameters of typical reverb rooms with considerably more detail
and realism.
4.2.1 Reverberation chambers
Reverberation chambers deliver the most natural form of reverb. In general, every room has its specific acoustic
properties which are not only dependent on its size but also on its shape (architecture) and the materials used
to construct it. For this reason, experts in architectural acoustics design rooms (concert halls, recording
studios, etc.) to produce a specific sound and reverb ambience.
Even today almost all recordings of classical music and a major part of jazz recordings are performed in a
dedicated recording room. Important professional studios sometimes have special reverberation chambers
tuned to produce a specific ambience. They can be built entirely from wood, ceramics or natural stones to
generate a specific sound in a very natural way. Some high-end studios even have facilities to adjust the walls
and ceilings so as to generate distinct reverb ambiences or sound images. However, as the cost of such rooms
are extremely high, newly built studios simply cannot afford a dedicated reverberation chamber. Understand-
ably, no reverb unit can produce reverberation that is more natural in character than the ambience generated by
a natural reverberation chamber. On the other hand, reverberation chambers do suffer from three decisive
drawbacks:
s
It is not possible to modify the reverb sound (except for rooms with adjustable walls and ceilings), so when
using natural reverb you cannot change its decay time or intensity.
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Natural reverberation chambers cannot be used to generate special surreal reverb phenomena, e.g. ex-
tremely long decay times or reverse reverb.
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Reverberation chambers are not portable! If you wish to use one particular reverb ambience, you will have to
record in the specific room that produces it. In a way, each reverberation chamber is unique.
4.2.2 Spring and plate reverb
Due to the disadvantages of natural reverb chambers (see section 4.2), two new methods of generating reverb
were invented and used in the 50s and 60s. For the first time ever, plate or spring reverb devices allowed for the
artificial production of reverberation. A reverb plate consists of a thin steel plate or sturdy metal sheet coated
with a gold alloy, which is set in motion by a generator radiating the signal to be processed (reverberated). At
another point somewhere on the plate, the signal is picked up by a transducer and then added to the original
signal. "Plate" reverb is quite natural in character because the vibrations of the plate are similar to air vibrations
4. TECHNICAL BACKGROUND
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