Improving the Morse Intercept Operator's Audio Display
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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This thesis improves the audio display for multiple Morse communications. Factors considered to improve the audio display are frequency of source, volume level of source, and methods of unmasking. The best frequency and volume level of a Morse source is 500 Hz at 70 dB sound pressure level. Two types of masking are researched frequency masking and expectation driven masking. Experiments showed by amplifying high pitched sources the effects of frequency masking are minimized. Other methods to compensate for frequency masking are 3-D sound and the placement of a source out of phase between the ears. Morse code recognition at 500 Hz is greatest when presented at the NO S-pi condition. Greatest unmasking for broadband signals occurs at 3-D locations between 60 and 90 deg where the largest ITD interaural time difference exists. This thesis theorizes and confirms that greatest unmasking of a source tone in 3-D sound corresponds to the spatial location that gives an ITD equal to a 180 deg phase shift for that tone. 3-D sound improves the performance of communication personnel who are required to monitor multiple speech communications. This thesis further provides 3-D cues for simultaneous Morse sources. Research focuses on improving accuracy and reducing fatigue. The criteria for improving cues are minimal fatigue and the highest copy accuracy. The presentation options are 2 channel diotic all sources in each ear , monaural each channel contains a unique source, information of a source is presented to only one ear , 3-D angles of 0, 10, 32, 45, 58, 69, and 82 deg. Experiments considered two and three simultaneous Morse signals. Results showed that 3-D sound does not improve accuracy when multiple sources are at equal volume level for the tested signal to interference ratio SIR.
- Voice Communications