The ASTi Telestra 4 architecture currently offers two flavors of the audio distribution interface unit, derived from preceding ASTi product-lines, the ACE-RIU and ACU devices. The ACE-RIU is the logical evolution from the industry-standard ASTi DACS Model Builder Remote Interface Unit (RIU), while the ACU is derived from the more recent Telestra 3 MBV Iris unit.

ASTi systems provide sophisticated voice communication and sound routing, synthesis, and modeling functions, generally used for simulation and training applications. In order to be useful, we need the ability to input and output the audio signals to the operators or interfaces of the system. Audio does not "travel well" in the analog domain, and passing low-level signals over distances greater than 25 feet is generally not recommended, hence it is desirable to move the analog interfaces out to the outer edges of the system boundary, and move the signals around in the digital domain.

This is where the ACE-RIU and ACU units step-up. These units provide input audio analog-to-digital, and output audio digital-to-analog conversion for audio signals, and support the Ethernet-based ACENet audio distribution protocol for the digital-side signals. Simply put, the ACE-RIU and ACU units provide the audio in/out interfaces, over a distributed Ethernet-based network. These interfaces are most often used as the connection point for operator headsets.

Looking to the ACE-RIU and ACU specifically, there is inevitably a significant overlap in functionality, since they are both designed to solve the same common functional capability, so below are some key differences including:

• Packaging
• I/O Support
• Serial Interfaces
• Input Audio
• Output Audio
• Microphone Power
• Device Power
• ACENet Network Connections
• Legacy System Updates
• New Programs
• Summary

The ACE-RIU presents 4 channels of audio I/O in a small form-factor stand-alone enclosure, and additionally may be efficiently rackmounted using a simple kit at a maximum density providing 12 channels of audio in 1U of rack space.

ACUs come pre-package in 1U rack-mount 19" chassis', in 2-, 4-, or 6-channel widths.

Each ACE-RIU channel supports a single digital input (closure sensing), and digital output (opto-isolated, solid-state relay). This works well with the basic ASTi PTT box, and live radio interfaces for the Synapse interface use-case.

Each ACU channel supports 3 analog inputs, and an opto-isolated digital output. The analog inputs may operate in a digital mode (contact closure sensing), or as a conventional 8-bit analog input. The ACU covers all the use-cases met by the ACE-RIU, and then some more. The ACU works well in situations where it is desirable to sense dual PTT inputs (radio and intercom), or where the operator interface is the ASTi 4-channel PTT selector switch box.

Each ACE-RIU supports 2 RS-422 serial ports per chassis, which can be used for ASTi HHT (Hand-Held Terminal) operator interfaces, or with ASTi SINCGARS panels.

The ACU units provide one RS-422 per fitted channel, so the 2-channel unit provides 2 serial ports, the 4-channel provides 4 ports, etc. These ports support the ASTi HHT and ASTi SINCGARS panel.

The audio input stages of both ACE-RIU and ACU are essentially equivalent, providing a fully electronically balanced input stage, however the gain ranges and method of setting them are different for the two devices.

The ACE-RIU input gain is set via hardware 'jumpers' which requires the case to be opened, and allows the gain to be set over the range 0 to 60dB.

The ACU input gain is set in software, and allows the gain to be set over the range -10 to +50dB.

The ACE-RIU output supports both differential and single-ended modes of operation (in single-ended mode, the available output voltage swing is halved compared to differential mode), and may drive down to an 8 Ohm load at approximately 1 Watt in differential mode, and 0.25 Watt in single-ended operation. The output stage is protected against shorting to ground. The output gain is fixed. In single-ended mode operation each channel provides two separately driven outputs, but it should be noted that each are exactly 180 degrees out of phase (generally this should not be an issue).

The ACU output is single-ended, and provides two independently driven outputs that are in phase, hence these may be connected together to provide greater current drive, or split to feed separate loads. The output can drive low impedance loads down to 8 Ohms at approximately 0.5 Watt, and is electronically protected against shorts to ground. The output gain may be adjusted in software over the range -23 to +20dB.

The ACE-RIU can provide 10V DC across the microphone lines. This requires the addition of a resistor pack inside the unit. If the input is operated in a single-ended configuration (as required by all commercial/civil and some military aviation headsets and microphones), the voltage available drops to 5V DC, which is typically below the recommended operating voltage for these devices.

The ACU provides software selectable power at 13.6V DC, and is available irrespective of the operating mode of the input stage (differential or single-ended), since power is applied to the positive microphone input pin.

ACE-RIUs and ACUs are powered using the same inline power "brick", providing 15V DC. The power supply input voltage range is 100-240V AC, auto-sensing. Note when rack-mounted each ACE-RIU requires an individual power-supply (3 "bricks" for 3 ACE-RIUs), hence 12-channels of audio input/output can be met with 3 ACE-RIUs (3 power supplies in 1U of rack-space), or 2 6-channel ACUs (2 power supplies and 2U of rack-space).

Both families of devices are driven using the ASTi ACENet Ethernet based audio distribution architecture, and each device requires a CAT5E cable.

One of the principal reasons for the existence for the two families of audio interface is to simplify the transition from previous generations of ASTi equipment to the latest.

The ACE-RIU is a direct replacement for the DACS/Model Builder TDM-card-driven RIU, and presents the same audio interface, via the front panel connectors. Therefore, an RIU may be disconnected and substituted with an ACE-RIU with no change to the audio and I/O cabling.

The ACU form-factor is a direct replacement for the packaged Iris units used with many Telestra 3 MBV systems, and presents the same audio interface, via the front panel connector.

Let’s say there is a requirement where the system is required to directly support an aviation class headset that has a single-ended powered microphone, which can only be supported with an ACU. Also applications where it would be advantageous to read more than a single-DI per operator in terms of I/O (such as those cases wishing to read both a Radio and Intercom PTT switch, or where the operator interface is an ASTi 4-channel PTT box), the ACU meets the need.

Beyond the above cases, the particular device selection probably comes down to a combination of factors. Some of the common considerations are highlighted in the following points:

• The ACE-RIU has a lower per-audio-channel cost ($1,750 for 4-channels with the ACE-RIU, versus $2,850 for the 4-channel ACU), but this may be offset by certain feature differences; for example each ACU channel provides a serial interface, whereas the ACE-RIU provides 2 serial channels per unit. So if the requirement is simply 4 serial interfaces, then the ACU works out cheaper (2 times ACE-RIU = 4 serial interfaces @$3,500), vs 1 times 4-channel ACU @ $2,850).
• The ACE-RIU is a truly stand-alone unit, and may conveniently be situated on a desk or workspace, while the ACU really belongs in rack enclosure.
• In terms of channel density the ACE-RIU can be rack-mounted in blocks of 3 using the rackmount kit, resulting in 12 channels of audio in 1U of rack-space, contrasted with 6-channel of audio in 1U of rack-space for an ACU.

In summary, the best advice is to contact one of the ASTi Project/Application engineers and discuss the specific project requirements. It may well be that, after reviewing the information, it becomes clear that one or the other of the audio peripheral devices is the obvious choice, and certainly we would be happy to provide our recommendations, after factoring in all the relevant considerations.