Mathur G., Tsangarakis M., Lotts D., Barry K., Agarwal N.

The military aircraft test and evaluation community generally uses the Modified Rhyme Test (MRT) method for evaluating speech intelligibility of the communication system. The MRT is conducted in the critical mission areas per Millitary, ANSI and/or ISO specifications. These standards specify that the MRT shall be conducted in a noise field that simulates the actual aircraft noise at the measurement location. Since the MRT method is based on the perception of words by listeners, it places no limitations on the characteristics of the sound system or the environment. Modern communication systems, however, incorporate several new electronic designs, e.g., automatic gain control, analog-to-digital (ADC) conversions that can introduce non-linearity in the system. This paper will present results of investigations conducted in a large military aircraft with high background noise levels. On this airplane, speech intelligibility in varying noise environment and with a moving speaker was evaluated. In flight MRT measurements were conducted to evaluate performance and qualification of new analog/digital PA systems. In these tests, emphasis was placed on 'relative' measurements between different system configurations and these results will be presented in this paper. The MRT was found to be most reliable method for the PA system qualifications when performed according to ANSI standards. Use of an alternative analytical method to measure speech intelligibility as a replacement for MRT will also be discussed.