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The audio mix modules are the core of the mixer unit. Each module shall
contain four eight-to-two attenuating mixer chips. These mixers shall
digitally controlled, and shall provide at least 63dB of attenuation
in 1dB steps, as per the high-level specification.
At this stage, it made sense to attempt to locate such a part, and indeed,
one was found. The SSM2163 from Analog Devices is such a
hybrid mixing device. It has respectable specifications, and is about $12
in quanitites between 10 and 100.
One output from each mixer chip is fed to a position on each output
bus. With the system in stock configuration with four mix boards,
one chip drives each output bus line. In larger configurations, up to
four mixer chips (from different mixer modules) may be attached to any
one output bus line. The remaining output from each mixer chip shall
be available for future upgrades such as inputs to DSP modules, etc.
Figure 20 depicts a mix module. A stock system
has only four of these boards, but up to sixteen may be used in a system.
Figure 20:
Mixer unit, audio mix module diagram. Systems shall have
four, eight or sixteen of these modules.
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Next: Bus Combiner Module
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Steve Richardson
2000-07-06
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