Algorithms; Random Hall - Lexicon 960L Owner's Manual

Using the Reverb Programs
In the early 1990s Dolby Digital, DTS, and MPEG surround
arrived. These systems provided discrete digital signals for
each channel and a separate Low-Frequency Effects
(LFE) that provided very low frequency sound effects.
Squeezing 5.1 discrete digital channels into a recording
involved some data reduction, but the reduction schemes
used psychoacoustical principles to make the resulting
artifacts less audible. Dolby Digital soundtracks were the
first to make the transition from movie theaters to the
home, via laser disc. With the advent of DVD, whose pop-
ularity rapidly eclipsed laser discs, Dolby Digital and DTS
tracks became more widely available for home theater.
The discrete digital technologies require specialized hard-
ware for playback, and the original source material can-
not be recorded on home tape recorders, VCRs, or broad-
cast over conventional broadcast equipment.
importantly more and more consumers were installing sur-
round sound systems in their homes, and there was a great
need for a technology that would allow standard two
channel recordings to be reproduced in a surround sys-
tem. Not with Dolby Pro Logic, which narrowed the front
image and provides a monaural surround signal, but with
a system that offered a wide front image over a large lis-
tening area, and the listener envelopment present in the
original recording location.
To solve both problems Lexicon developed Logic7 matrix
technology, which provides a method for releasing sur-
round recordings on standard stereo compatible CDs.
More importantly, Logic7 and LexiconLogic provide a
method of playing the millions of standard two channel
music recordings with all the advantages of discrete sur-
round.
Logic7 also allows Dolby surround films to be played with a
wide frontal image and full rear envelopment.
encoded recordings can be broadcast or played on any
currently available reproduction equipment, and yet they
provide full five channel surround on a device with a
Logic7 decoder, and decent four channel surround when
played with Dolby Pro Logic. Logic7 uses matrix technolo-
gy to compress the spatial aspects of a recording so it can
be delivered on a two channel format. There is no data
reduction of the sound waveforms themselves, so the
sound quality can be very high.
Competing with Logic7 and the current data-reduced dis-
crete technologies are two audio disc formats based on
DVD technology, DVD-Audio and SACD. These promise to
deliver discrete 5.1-channel surround without data reduc-
tion. These encoding technologies promise higher fidelity
than CD, thanks to 96-kHz/24-bit recording—a signal for-
mat for which the 960L is already prepared. The eight-
channel design and modular construction of the 960L
make it ready for future surround advances, whatever
they may be.
5-8

ALGORITHMS

Random Hall

Random Hall is a hall effect with gradual build-up, well suit-
ed to complex sounds like orchestral music. Its reverbera-
tors change over time in controlled random ways to avoid
the buildup of tinny, grainy, metallic, or other colorations.
The early reflections are user adjustable in amplitude and
delay. Some skill is needed to set useful reflection pat-
terns. Since the reflections are adjustable, they are not
randomized. Once set, the reflection pattern is fixed. The
pattern can be expanded or contracted in time using the
"Delay Master" control, and the overall level of the pattern
can be set with the "Early Level" control.
More
The most important user parameters for Random Hall are
the level controls – the "Early Level" and "Reverb Level".
Early Level is a master control for all the early reflections.
Lowering the control to zero eliminates the reflections, and
their associated sense of distance from the sound source.
The "Reverb Level" control is a master control for the late
reverberation. With this control you can set the exact
amount of reverberance and envelopment.
The apparent size of the space supplied by the late rever-
beration is set with the Shape, Spread, and Size controls.
Of these controls the Shape and Spread are the most nat-
ural. As Shape is raised from zero to about 30% the onset
of the late reverberation goes from abrupt to gradual. The
effect on the apparent size of the space is quite dramat-
ic. Spread has little or no effect until Shape is at about a
quarter of its range, at which point Spread affects the
length of both the buildup and sustain. At this point, the
sustain will be approximately the time value indicated by
the Spread display, in milliseconds. At still higher settings of
Logic7
Shape, a secondary sustain appears in the envelope at a
lower level; this simulates a very diffused reflection off the
back wall of the hall, helping to create a sense of size and
space. This reflection becomes stronger and stronger,
reaching optimal loudness when Shape is at about 2/3 of
its range. The highest Shape settings are typically used for
effects. Near the top of the scale, the rear hall energy
buildup becomes stronger than the earlier part of the
envelope, an effect used to create an inverse sound (see
Reverse).
To avoid colorations, the signal is randomized by the Spin
and Wander parameters. The randomizers controlled by
the Spin and Wander parameters principally affect the
perceived acoustics of the space. High settings can be
used to break up small-room modes, as when recording a
voice-over in an announce booth, but extreme settings
can have pitch effects.
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