GALILEO 616: PROCESSING
Processing Functions
Providing up to two seconds of delay for each input and output represents
just the beginning of Galileo 616’s power; it is the unit’s
filtering that truly sets it apart in the realm of DSP-based loudspeaker
management systems. Each input and output includes a careful digital implementation
of Meyer Sound’s famous CP-10 complementary phase parametric equalization
(five bands on inputs, ten bands on outputs), coupled with our new TruShaping
program filters. This unique combination gives users the ability to treat
acoustical problems appropriately and accommodate subjective needs without
creating excessive phase shift that can degrade intelligibility and signal
clarity.
Galileo 616 supplies a powerful signal processing
arsenal incorporating delay and many forms of filtering. Shown above is
the Compass screen that configures Galileo 616’s Composite EQ, available
on each input and output.
Also supplied in Galileo 616 are digital implementations of the subwoofer
crossover, air absorption compensation, and M Series array compensation
filters first realized in the LD-3 compensating line driver.
Galileo 616’s all-digital design also enables Meyer Sound to give
users entirely new capabilities, like low frequency coverage shaping for
widening low-frequency dispersion patterns. A library of coverage-shaping
presets is provided for large-scale M Series products, such as the MILO
high-power curvilinear array loudspeaker and M3D line array loudspeaker.
Composite EQ Filter Architecture
Proper sound system design, implementation and alignment can avoid a
host of problems in system response, and this should always be the first
line of pursuit in sound reinforcement. When all possible measures in
these areas have been taken, however, there are usually some problems
that remain. Equalization is a primary tool for dealing with such problems.
Tuning a modern sound system with equalization is a complex task breaking
down to a few basic needs: subjective shaping of the system frequency
response, compensating for air attenuation and correcting for some anomalies
resulting from interactions between loudspeakers or between loudspeakers
and the acoustical environment. (This last category would include low-frequency
buildup, for example.) But there are fundamental differences in character
between some of these needs, which define a requirement for different
tools to do the jobs appropriately. Failing to account for these distinctions
can result in severe degradation of system phase response, with corresponding
reductions in intelligibility and clarity of the sound.
Galileo 616’s Composite EQ filter architecture is intended to address
this issue and provide the most potent equalization system available in
any current digital loudspeaker management system, while keeping phase
shift to the lowest amount practically attainable.
Let’s take a closer look at the problem and how Composite EQ solves
it.
Interaction-based effects are, classically, second-order phenomena that
produce ripple in the measured frequency response of a system. Using Meyer
Sound’s SIM 3 audio analyzer, these artifacts can be clearly seen.
In practice, there are many interactions for which equalization is not
the most effective approach, but for those that do yield to equalization,
the best tool for attacking them is a fully parametric equalizer producing
both amplitude and phase responses complementary (that is, equal and inverse)
to the characteristics of the interaction artifact being treated. Meyer
Sound’s CP-10 complementary phase parametric equalizer’s second-order
filters were created for this purpose, and Galileo 616 incorporates a
careful digital implementation of a CP-10 filter set on each input and
output. When such an equalizer is properly configured, the effect of treatable
interactions can be essentially removed from the system response, leaving
both amplitude and phase responses quite flat.
Subjective shaping and interaction effects like low-frequency buildup,
on the other hand, tend to be much broader in shape. High-order filters
are ill suited to this sort of gentle amplitude response shaping and,
as well, generate considerably greater phase shift than low-order filters.
Compass Software: White line indicates
phase
Galileo 616’s Composite EQ provides the right tool for these jobs,
too: the TruShaping equalizer. The TruShaping equalizer (patent pending)
is a digital implementation of Meyer Sound’s acclaimed VX-1 program
equalizer, extended to contain four first-order interactive filters in
an innovative configuration. Since the TruShaping EQ’s filters are
low-order, they keep phase shift to a minimum, preserving the integrity
of the signal. In fact, the unique cascading topology used to create the
TruShaping equalizer allows the bands to overlap, which results in slopes
as low as 3 dB per octave and response curves so smooth they could not
be obtained any other way. Even with extreme settings, the TruShaping
equalizer will rarely result in even so much as 45 degrees of phase shift.
No other device currently on the market offers this approach.
This technique is so successful for system frequency response shaping
applications that the Array Compensation filters in Meyer Sound’s
Galileo 616 are based on the TruShaping filter topology.
As Meyer Sound self-powered systems are optimized to produce flat frequency
and phase response when they ship from the factory, the TruShaping equalizer
provides a powerful tool for adding “warmth,” “presence”
or other subjective qualities.
Composite EQ, by providing both CP-10 complementary phase parametric
and TruShaping low-order shaping equalization, gives the user the right
tools to deal with both acoustical anomalies and subjective needs. Best
of all, the Composite EQ user interface in the Galileo system’s
Compass control software presents a clear picture of the resulting equalization
by overlaying the CP-10 and TruShaping responses being applied, both amplitude
and phase, in a single editable graphical display. EQ parameters can be
edited directly by simply dragging in the display, or edited numerically
for greater precision.
Air Absorption Compensation
As sound waves travel long distances through air, high frequencies are
absorbed, a fact important to consider when setting up high-powered loudspeakers
for a long-throw application. But the effect of air absorption on sound
is complex to describe, as it depends on a number of factors, including
distance, temperature, humidity and altitude. The equations shown here
are used to calculate the sizable tables upon which Galileo 616 draws
to provide its atmospheric compensation filtering.
Method for calculating frequency dependant
air absorption from ANSI S1.26-1995. |
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