Once Aim 1 is complete and effective NMTD settings have been identified, we will initiate a Phase II NMTD trial to assess efficacy and tolerability. The primary outcome variable will be AHI reduction by NMTD compared with CPAP during a repeat polysomnogram (PSG). We will randomly assign previously titrated CPAP vs. NMTD to each subject then compare the resultant AHI between the two devices. Tolerability will also be assessed by sleep efficiency, arousal index, and sleep architecture. While auditory stimuli below 90 dB threshold should not adversely affect sleep architecture and quality,1 intermittent stimuli given during different sleep stages have not been previously assessed. Therefore, we will monitor NMTD's influence on sleep architecture, arousal index, and sleep efficiency compared to the same variables during CPAP use, allowing us to examine whether NMTD affects sleep quality. We will also assess patient preference in using CPAP versus NMTD.