Section 874.3330 - Master hearing aid(a)Identification. A master hearing aid is an electronic device intended to simulate a hearing aid during audiometric testing. It has adjustable acoustic output levels, such as those for gain, output, and frequency response. The device is used to select and adjust a person's wearable hearing aid.(b)Classification. Class II (special controls). The device is exempt from the premarket notification procedures in subpart E of part 807 of this chapter subject to the limitations in § 874.9 .51 FR 40389, Nov. 6, 1986, as amended at 84 FR 71813 , Dec. 30, 2019