Vocoder Development Support Tool:

The VDST performs voice encoding/decoding using the NEXCOM standard ATC-10B vocoder algorithm developed by Digital Voice Systems, Incorporated (DVSI).

The VDST supports easy integration with other NEXCOM equipment by supplying both linear and compressed digital voice on a single, multi-slot synchronous serial interface (SSI). Unlike the commercial hardware from DVSI, the VDST supports “truncated mode” by providing compressed voice at a rate of 4000 bits per second (bps) compared to 4800 bps for normal mode. By providing a quick solution to the issues above, the VDST facilitates ongoing R&D activities as an interim measure that reduces or eliminates the impact of Vocoder development delays on the overall program schedule.

Key features of the VDST are:

Guaranteed Interoperability: Avionics vendors and other developers now have a common implementation to base their work upon, ensuring interoperability now without waiting for a “bit-exact” version of the Vocoder to be completed.

Preferred Interface: Integration with avionics and ground system equipment is simplified by the utilization of a single, DSP-type, high-speed synchronous serial port.

Truncated Mode: The VDST implements truncated mode by a method which is transparent to the user. Initially, the clock-slow down option has been implemented using a set of digital phase-locked loops (DPLLs) and digital resamplers.

Availability:  Because of CIE’s expertise in previous efforts involving development, integration and testing of a number of interfaces with the DVSI VC-20, development and implementation of the VDST was completed much earlier than other alternatives.

The VDST is implemented with a DVSI VC-20 assembly, complemented with an Intelligent Interface Module (IIM). The IIM uses a dedicated DSP with embedded FLASH and custom timing circuitry. It interfaces to the DVSI card using a serial PCM (uncompressed voice) format and provides a custom nibble interface at 9600 nibbles/second for Vocoded voice.  The VC-20 is slaved to the clocks generated by the IIM. The unit is packaged in a small enclosure (1.5 x 4.2 x 6.4 inches) and is powered by a wall mounted supply.

CIE Engineering, Inc. • 6001 Woodlake Lane • Alexandria, VA 22315 • Phone: (703) 922-7061