The Lincoln Laboratory-Aerospace Medical Research Laboratory digital speech test facility

A narrowband digital speech communication test facility has been established and operates between Lincoln Laboratory and the Wright-Patterson Aerospace Medical Research Laboratory. Noise fields simulating the acoustic environments of E3A and F-15 aircraft are established and Air Force personnel use the link operating at 2400 bps with a vocoder designed at Lincoln Laboratory, and a commercial telephone line modem. The facility includes a digital signal processing computer which can introduce bit errors and delay into the transmit and receive data. Communication scenarios are used to exercise the vocoder-modem channel with the dynamics and vocabulary of typical operational exchanges. Answers to a standard questionnaire provide acceptability data for the 2400 bps JTIDS class 2 voice channel. For the tests run so far, the 2400 bps voice is acceptable in the sense of positive user response to the questionnaire. Further testing using error and delay simulations will follow. An F-15 to F-15 link will be simulated at AMRL using a pair of vocoders operating back-to-back and in separate noise chambers.