Method and apparatus for distortion product emission testing of hearing

Abstract

Apparatus and method are disclosed for the recording of distortion product emission (DPE) levels in human beings. At least one microphone and a sound-delivery system is inserted in the external ear canal in a manner similar to that required to position a small hearing aid. Two primary tones T f1 , T f2 are applied simultaneously to the ear. The cochlea of the inner ear produces a DPE tone which is sensed by the microphone. DPE levels are sensed as a function of input frequencies f 1 and f 2 . Such DPE frequency is equal to 2f 1 -f 2 . Such DPE frequencies are collected in 100 Hz steps by adjusting f 1 and f 2 and maintaining a substantially constant ratio between f 1 and f 2 . Two output forms are created: an DPE audiogram and a DPE input/output function. Noise picked up by the microphone is reduced by averaging the DPE signal many times, yet causing each of the DPE signals that is averaged to be of the same phase as every other DPE signal. Random phase noise is reduced by the averaging process. Body noise may be reduced by using two microphones and applying the output of one such microphones to the plus input of a differential amplifier. The output of the other less sensitive microphone, after amplification and phase adjustment is applied to the negative input of such differential amplifier. The output of such amplifier results with the body noise signal substantially reduced, but with the DPE signal substantially unchanged. This abstract of the disclosure-is not intended to define the scope of the invention.