The Audio Interface Unit (AIU) provides audio input/output amplification for handsets, headsets, and speakers via the RIU. The unit developed for the panels was based on our previous AIU unit and included jumper- adjustable input/output gain settings and a 1 watt speaker amplifier; but it also included support for binaural headsets, and both differential and single-ended handsets. The combination of on-board design with proper audio connector configuration allowed most of the panels to operate interchangeably using either the SHINCOM-style binaural headset or the telephone-style handset.

Since the gain level of the AIU is fixed, volume control is performed by varying the input signal level from the RIU.

ASTi already offered a keypad with LED readout device to provide a generic communications control panel. Early design reviews with the Canadian Navy indicated that minor changes to the keypad and the state machine would make it suitable as a control panel for the instructor/gameplayers.

Based on operations manuals and discussions with end-users of the equipment, ASTi produced state machine software, running on the Model Server platform, and supporting each of the system panels. Due to the selection of the Linux operating system and its support for true multi-tasking, we were able to create multiple instances of each state machine, where one instance corresponds to one individual panel. By allowing a small value change to a configuration file to control the number and mapping of state machine instances, true system flexibility and scalability was employed. This allows the future third cubicle to be supported within the state machines by simply restarting with the new configuration file.

A conceptual overview of the state machine design is presented in Figure 6.

The record and playback system supports 30 simultaneous audio record streams (8 kHz, 8 bit mu-law). It included all of the pre-programmed internal nets for each of the cubicles (14 total) and 16 external radio nets which are dynamically definable by the host computer, with respect to frequency and mode during the game.

Each of these 30 record streams is received directly from the DIS audio network interface connecting the system, and have a total capacity of more than 8 hours record time. Each is time-indexed for commanded playback at precisely the desired location.

Since there was a requirement for simultaneous record and playback capability (i.e. a training session could occur within the training areas while a debrief session was occurring simultaneously), we provided two identical Record/Playback systems, with full and dynamic host control of each system. Playback audio can be routed to a single instructor station in order to independently prepare the playback sequence, or routed out of the 60 watt PA system for broadcast within the debriefing area.

Additionally, tape back-up capability is provided for exercise archival purposes.

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