The USB-300-I differentiates
the USB-300 by having the option of using Insert EarTone (it
is also possible to employ Peltor headset with TDH-39
phones). The audiometer supports 4 automatic hearing tests
(20 dB, 20 dB Random, XX dB Random and Hughson Westlake).
Furthermore you can deactivate frequencies, which is useful
if you have one or more frequencies that are not tested.