Method and apparatus for distortion product emission testing of hearing

• US 5,664,577 A
• Filed: 06/13/1996
• Issued: 09/09/1997
• Est. Priority Date: 01/25/1990
• Status: Expired due to Fees

• Current Assignee: Baylor College of Medicine (Baylor College)
• Original Assignee: Baylor College of Medicine (Baylor College)
• Inventors: Martin, Glen K., Lonsbury-Martin, Brenda L.
• Primary Examiner(s): Hayes, Gail O.
• Assistant Examiner(s): Poinvil, Frantzy
• Application Number:
  US08/662,881
• Time in Patent Office: 453 Days
• Field of Search: 128/746, 73/585, 73/587, 73/801, 381/25, 381/23.1
• US Class Current: 600/559
• CPC Class Codes: A61B 5/12 Audiometering
• CPC Class Codes: A61B 5/121 evaluating hearing capacity

Abstract

Apparatus and method 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. 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 f₁ and f₂. Such DPE frequency is equal to 2f₁ -f₂. Such DPE frequencies are collected in 100 Hz step by adjusting f₁ and f₂ and maintaining a substantially constant ratio between f₁ and f₂. Two output forms are created: an DPE audiogram and a DPE input/output function. Noise picked up is reduced by averaging the DPE signals many times, yet causing each of the DPE signals that is averaged to be of the same phase a 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 such amplifier results with the body noise signal substantially reduced, but with the DPE signal substantially unchanged.

Claims

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

signal generating means for generating a first electrical signal of frequency f₁ and a second electrical signal of frequency f₂, the frequency f₂ being greater than the frequency f₁,

first and second earphones responsive respectively to said first and second electrical signals for producing a first tone of frequency f₁ and a second tone of frequency f₂,

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 2f₁ -f₂,

digital computer means for controlling said signal generating means to produce a plurality of sets of signals of frequency f₁ and f₂ where the ratio of such frequencies f₂ /f₁ 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 2f₁ -f₂ corresponding to each of said sets of frequencies f₁, f₂, and

plotting means responsive to said digital computer means having stored therein tone levels at frequencies of 2f₁ -f₂ for plotting said levels of each of said tones at frequency of 2f₁ -f₂ as a function of frequency equal to the geometric mean of the frequencies f₁ and f₂.

2. A method for reducing noise in distortion product emission testing comprising the steps of:

generating a steady state electrical signal representative of the distortion product emission (DPE) tone from an ear, said DPE tone being of constant amplitude, frequency and phase, said steady state electrical signal being contaminated by random phase noise,

repeatedly initiating a time sample having a length which does not drift with respect to the period of said DPE tone to produce a plurality of time samples, and

applying said plurality of time samples to a Fourier-transform spectrum analyzer to determine an averaged spectrum to determine the amplitude level of said DPE tone, whereby noise is reduced.

3. A method for reducing noise in distortion product emission testing comprising the steps of

generating a first steady state oscillating signal of frequency f₁ and a second steady state oscillating signal of frequency f₂ and a triggering signal of frequency 2f₁ -f₂ such that said first signal, said second signal and said triggering signal have substantially no phase drift among any of such signals,

applying said first steady state oscillating signal of frequency f₁ and said second steady state oscillating signal of frequency f₂ to the ear canal of the outer ear of a human being,

generating a steady state electrical response signal representative of the distortion product emission tone (DPE) of substantially constant amplitude and phase of frequency 2f₁ -f₂ which is generated in the ear in response to said first and second signals, said steady state electrical response signal being contaminated by random phase noise,

dividing said steady state electrical response signal by reference to said triggering signal into a plurality of equal length time segment DPE signals such that each DPE signal of frequency 2f₁ -f₂ begins with the same phase, and

applying a predetermined number of said equal length time segments to a Fourier-transform spectrum analyzer to determine the amplitude level versus DPE frequency averaged spectrum, whereby said amplitude at said frequency 2f₁ -f₂ of said averaged spectrum substantially represents the level of said DPE tone and the noise level is substantially reduced.