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 Sr condition. 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 1800 phase shift for that tone. Ames Research Center has demonstrated that 3-D sound improves the performance of communication personnel who are required to monitor multiple speech communications. This thesis supports that result and further provides 3- D cues for simultaneous Morse sources.
Research focuses on improving accuracy and reducing fatigue rather than increasing intelligibility.
Fatigue is measured by subjects choice of which presentation option is easier to copy. The criteria for improving cues are minimal fatigue and the highest copy accuracy.