Method and apparatus for distortion product emission testing of hearing

Apparatus for distortion product emission audiogram testing of a human being comprising,

• signal generating means for generating a first electrical signal of frequency f.sub.1 and a second electrical signal of frequency f.sub.2, the frequency f.sub.2 being greater than the frequency f.sub.1,
• first and second earphones responsive respectively to said first and second electrical signals for producing a first tone of frequency f.sub.1 and a second tone of frequency f.sub.2,
• an eartip adapted for insertion in the ear canal of the outer ear of said human being, said eartip having first and second audio tubes terminated therein which are connected respectively to said first and second earphones which transmit said first tone and said second tone to said ear,
• said eartip including a microphone with a first output lead connected thereto,
• signal analyzing means responsive to said first output lead connected to said microphone for generating a signal corresponding to a level of a tone generated in the ear of said human being at a frequency of 2f.sub.1 -f.sub.2,
• digital computer means for controlling said signal generating means to produce a plurality of sets of signals of frequency f.sub.1 and f.sub.2 where the ratio of such frequencies f.sub.2 /f.sub.1 is approximately the same for each set of signals, and responsive to said signal analyzing means for recording each level of said tone at frequency of 2f.sub.1 -f.sub.2 corresponding to each of said sets of frequencies f.sub.1, f.sub.2, and
• plotting means responsive to said digital computer means having stored therein tone levels at frequencies of 2f.sub.1 -f.sub.2 for plotting said levels of each of said tones at frequency of 2f.sub.1 -f.sub.2 as a function of frequency equal to the geometric mean of the frequencies f.sub.1 and f.sub.2.