DSP Input Equalization
By the application of digital filters for equalization, the
MPM4 achieves perfect matching and repeatability of
equalization that cannot be achieved with analog filters.
The equalization curves are modeled after analog
equalizers to give the smooth response expected from
analog equalizers.
DSP Output Equalization
The output equalizers are similar to the input in design, yet
with different curves. The curves chosen for the output are
models of the analog equalization in Whirlwind's
acclaimed MPM1. The bass curve is especially effective
for adding bass to small speakers such as those used
typically in ceilings.
DSP Source To Zone Routing
Source to Zone routing behaves like a selector switch for
each Zone to select the chosen input. Unlike a simple
switch, the MPM4 always switches signals with fades
instead of hard switching. This removes any artifacts such
as clicks or pops when a different input is selected.
DSP Priority Chain
The Priority handling of the MPM4 is one of the features
that makes the system unique and versatile. Each Priority
is handled separately and independently. Higher priority
inputs will duck both input sources as well as lower priority
signals. Zones that are not selected for a given priority
remain unaffected when a priority is active. Lower
numbered Priorities have the highest priority. The ducking
hierarchy is:
P1 > P2 > P3 > P4 > Program Source
so that higher priority inputs duck the program source and
any lower priorities that are active when the higher priority
occurs.
DSP Priority Signal Detection
Signal level detection for Priority Inputs is independent of
the signal detectors used for clipping and level detection.
This allows different time constants, optimized for each
application to be used in each of the signal detectors.
DSP Priority Ducking
When a Priority input becomes active, any program signal
present (or lower active priority signal) is faded down
quickly and smoothly to the duck attenuation level where it
remains while the priority is active. When the Priority
becomes inactive, the ducked signal returns slowly and
smoothly back to its level prior to ducking. The delay and
slow release means there will be no chattering or other
artifacts as a result of the Priority switching off, even when
the priority itself may turn on and off due to the source not
changing cleanly, for example, noises due to handling a
microphone after an announcement.
DSP Priority Gating
Priority Inputs with levels below their threshold of being
active are gated off. This keeps any noise from the Priority
Input sources from bleeding to the outputs. If, during
setup, the installer desires to hear un-gated Priorities, this
may be done in Priority Assign mode. In Priority Assign,
the selected Priority Input is forced on, and, other priorities
are forced off. This means that the Priority signal is routed
through to the outputs un-gated.
DSP Priority Output Levels and Priority Override
Priority Levels may be adjusted in Priority Assign mode to
set the level of each channel of priority audio within each
zone relative to the Source Inputs. When Priority Zone
Level Override has been turned on for P1 or P2, the Zone
Volume Controls are bypassed and inactive, but Zone Max
Level is still in effect.
Remote Control
The MPM4 provides Remote control inputs for each of its
four zones. A low power 12V source is provided for each
Remote. Communication to the remotes is handled with
half duplex communication over RS485 at 9600 baud. The
protocol for communicating with remotes is proprietary.
The main unit polls each of the remotes and waits for a
response. Remotes never initiate communication. This
very conservative design allows the remotes to work with a
range of up to 1500 ft of CAT-5 cable.
Non-Volatile Settings Memory.
The MPM4 employs a small EEPROM to store front panel
settings in the event power is lost. When the unit sits with
no interaction for a period of time, it checks to see if any
controls have changed since the last time settings were
saved. If changes have occurred, the new settings are
saved in the EEPROM.
The EEPROM is divided in to 2 regions, system and user.
As described, the MPM4 saves user settings whenever
there are changes and an inactivity period times out.
These are stored in the user memory region. The second
region is used only for storing setup parameters and is only
written to when the installer locks the unit. The concept is
that the system region is used infrequently, where as the
user region is used as frequently as every time the user
changes a zone source or level. EEPROMs have a limited
life. However, even with the user region frequency of
writes, it is expected that the EEPROM will last 30 years
minimum. In the event that there is a failure reading from
the user region, the system will load the last settings saved
in the system region. This assures that the system will
always have a set of useful settings to use on power up.
Power and Thermal
The MPM4 employs a universal input switching supply.
This allows the system to operate over a wide variety of
power voltages, 100 to 250VAC. This supply also
produces less heat because of its efficiency as well as
reducing weight compared to a non-switching supply. A 2-
speed fan is employed to assure that the system remains
cool. At room temperature with no signals present, the
fans will generally remain off, or at low speed. For most
environments and applications, the fan will only need to
run at its low speed. In high ambient temperatures, the
high-speed mode may activate. Keeping the system in a
cool environment and keeping the fan inlets and vent
openings unobstructed helps assure a long uninterrupted
service life for the MPM4.
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