Specifications

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SymNet Technologies for Audio
Distribution
As mentioned earlier, SymNet’s toolkit has a full
complement of routing, mixing and matrixing modules.
However, several of its audio processing modules are of
particular use in audio distribution systems.
AGC (Automatic Gain Control) modules are invaluable
for controlling the sometimes wildly varying levels of
background music sources. The British EQ combines the
most popular filters and equalization used in microphone
processing. When combined with a Compressor/Limiter,
triggering a Ducker, you’ll have a foolproof paging signal
chain that simply sounds great.
In certain situations an audio distribution system must
perform tasks at specific times. SymNet accommodates
this by scheduling a preset recall on a calendar. Using the
Event Scheduler in SymNet Designer, the integrator can
setup any stored preset to be recalled at a specified time.
Recurring, or exclusive, special events are easily
accomplished as well.
By far the most invaluable and unique process SymNet
has to contribute to the performance of audio distribution
systems are the SPL Computer modules. Their discussion
follows as the featured technology for this application.
G SPL Computer Modules
SymNet SPL Computer Diagram
Sometimes referred to as Ambient Noise Compensation
modules, SPL Computers use a microphone to sense
the level of ambient (crowd) noise in a room, then auto-
matically adjust the volume of the sound system within
predetermined parameters. Following the success of its
stand alone SPL Computers (the 571/572 and 371/372),
Symetrix has incorporated the technology into SymNet
by developing SPL Computer DSP modules for
SymNet Designer.
A sensing microphone is mounted in the zone to monitor
the ambient noise level within that zone. Typically, one
SPL Computer and microphone are required for each zone
where ambient noise compensation is desired.
As more people are added to the zone the room volume
increases; the SPL Computer module turns up the volume
within the zone to maintain the proper balance of ambi-
ent noise and sound system volume. As the room empties
(reducing the ambient noise level), the SPL Computer
turns the sound system down to an appropriate level. In
SymNet Designer, there are two types of SPL Computer
modules: ‘Gap Sensing’ and ‘Continuous’. Both types use
a microphone to monitor the ambient level in the room,
but they differ in how they perform the measurement.
G SPL Computer Modules: Gap-sensing
SymNet Gap-sensing SPL Computer module
To take a measurement of the ambient noise, the Gap-
sensing SPL Computer either waits for the audio playing
in the zone to stop or fall below a certain threshold.
Once the audio has fallen beneath the threshold, the SPL
Computer mutes the zone audio and takes a reading of
the room. Based on the measured level, the volume is ad-
justed then the audio is un-muted. The level in the zone
will then be appropriate. If there are no gaps in the audio,
the system will momentarily mute the audio at specified
intervals to take its reading.
This type of SPL Computer module often produces better
results than a continuously sensing version as it does
not have to extrapolate its own output from the ambient
noise. Therefore, it can be more accurate and predictable
in certain situations as well as more forgiving to non-