Method and apparatus for distortion product emission testing of heating
First Claim
1. Distortion product emission apparatus 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 arranged and designed insertion in the ear canal of the outer ear of a 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 first microphone means with a first output lead connected thereto for generating a first electrical signal on said first output lead which is proportional to a distortion product emission tone generated in the ear of said human being at a frequency of 2f1 -f2 and to other body noises,said eartip including a second microphone means with a second output lead connected thereto for generating a second electrical signal on said second output lead which is proportional to said other body noises but is not substantially proportional to distortion product emission tone generated in the ear of said human being at a frequency of 2f1 -f2,differential amplifier means responsive to said first and second signals for generating a differential signal proportional to the differences between said first and second electrical signals on a third output lead on which said distortion product emission tone at a frequency of 2f1 -f2 is present, but noise signals due to body noises of said human being have been reduced, andsignal analyzing means responsive to said differential signal on said third output lead for generating a level signal corresponding to said distortion product emission tone generated in the ear of said human being at a frequency of 2f1 -f2.
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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 Tf1, Tf2 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 steps 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 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.
50 Citations
13 Claims
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1. Distortion product emission apparatus 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 arranged and designed insertion in the ear canal of the outer ear of a 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 first microphone means with a first output lead connected thereto for generating a first electrical signal on said first output lead which is proportional to a distortion product emission tone generated in the ear of said human being at a frequency of 2f1 -f2 and to other body noises, said eartip including a second microphone means with a second output lead connected thereto for generating a second electrical signal on said second output lead which is proportional to said other body noises but is not substantially proportional to distortion product emission tone generated in the ear of said human being at a frequency of 2f1 -f2, differential amplifier means responsive to said first and second signals for generating a differential signal proportional to the differences between said first and second electrical signals on a third output lead on which said distortion product emission tone at a frequency of 2f1 -f2 is present, but noise signals due to body noises of said human being have been reduced, and signal analyzing means responsive to said differential signal on said third output lead for generating a level signal corresponding to said distortion product emission tone generated in the ear of said human being at a frequency of 2f1 -f2.
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3. Distortion product emission apparatus 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, said first and second signals having substantially equal amplitude levels, 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 arranged and designed insertion in the ear canal of the outer ear of an 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 first microphone of high signal sensitivity with a first output lead connected thereto, and a second microphone of low signal sensitivity with a second output lead connected thereto, said first microphone being sensitive to small amplitude DPE signals of frequency 2f1 -f2 and to contaminating large amplitude signals caused by coughs and the like whereas said second microphone is not sensitive to said small amplitude DPE signals of frequency 2f1 -f2 but is sensitive to said large amplitude body-induced signals, differential amplifier means having positive and negative input terminals to which said first output lead and said second output leads are connected for subtracting the respective signals on said first and second output leads to produce a DPE signal on an output lead with reduced contamination due to said large amplitude signals.
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6. Distortion product emission apparatus comprising,
signal generating means for generating a first steady state oscillating signal of frequency f1, and a second steady state oscillating signal of frequency f2, the frequency f2 being greater than the frequency f1, said first and second signals having substantially equal amplitude levels, means for synchronizing said first and second signals such that there is substantially no phase drift between said first and second signals, first and second earphones responsive respectively to said first and second signals for producing a first tone of frequency f1 and a second tone of frequency f2, an eartip arranged and designed for insertion in the ear canal of the outer ear of a human being, said eartip having first and second audio tubes 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, said microphone generating an output signal on said first output lead which includes random phase noise and a steady state oscillating distortion product emission (DPE) tone generated in the ear of said human being, said distortion product emission (DPE) tone being a sinusoid of substantially constant amplitude and phase with a frequency of 2f1 -f2, means coupled to said signal generating means for generating a triggering signal which is of substantially the same frequency and phase as that of said DPE tone of said output signal, a signal analyzer including (i) time averaging means for time averaging said output signal prior to spectral analysis of said output signal, said time averaging means including means responsive to said output signal and to said triggering signal for time averaging said output signal by separating said output signal into a plurality of equal length time segments such that the DPE tone component of frequency 2f1 -f2 of said output signal begins with the same phase in each time segment, and means for averaging said equal length time segments to produce an averaged signal, and (ii) a Fourier-transform spectrum analyzer means responsive to said averaged signal for determining the amplitude versus frequency spectrum of said averaged signal, whereby said amplitude at said frequency 2f1 -f2 substantially represents the level of the DPE tone and the noise level is substantially reduced.
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8. 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, averaging said DPE signals over a predetermined number of time segments to produce an averaged signal, and applying said averaged signal to a Fourier-transform spectrum analyzer to determine the amplitude level versus DPE frequency spectrum of said averaged signal, whereby said amplitude at said frequency 2f1 -f2 substantially represents the level of said DPE tone and the noise level is substantially reduced.
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9. Distortion product emission apparatus comprising,
first 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, such that the phase of the first and second signals do not substantially drift with respect to each other, second signal generating means for generating an oscillating triggering signal of frequency 2f1 -f2, the phase of which does not substantially drift from that of said first electrical signal of frequency f1 or that of said second electrical signal of frequency f2, 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 arranged and designed for insertion in the ear canal of the outer ear of a human being, said eartip having first and second audio tubes 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, said microphone generating an electrical signal on said first output lead which includes random phase noise and a distortion product emission tone being a sinusoid of substantially constant amplitude and phase with a frequency of 2f1 -f2, a signal processor including (i) time averaging means responsive to positive going zero crossing times of said triggering signal for time averaging said signal on said first output lead by separating said signal into a plurality of equal length time segments such that the distortion product emission tone of said signal begins with the same phase in each time segment and averaging said equal length time segments to produce an averaged signal, and (ii) a spectral analyzer including a Fourier-transform spectrum analyzer, and means for applying said averaged signal to said Fourier-transform spectrum analyzer for determining an amplitude versus frequency spectrum of said averaged signal, whereby said amplitude at said frequency 2f1 -f2 substantially represents the level of said distortion product emission tone and the noise level is substantially reduced.
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10. Distortion product emission apparatus comprising,
signal generating means for generating a first electrical sinusoidal signal of frequency f1, a second electrical sinusoidal signal of frequency f2 and a third electrical square-wave signal of frequency 2f1 -f2, where said first, second and third signals have substantially no phase drift among them, 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 a human being, said eartip having first and second audio tubes 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, said microphone generating a fourth electrical signal on said first output lead which includes random phase noise and a distortion product emission tone generated in the ear of said human being, said distortion product emission tone being a sinusoid of substantially constant amplitude and phase with a frequency of 2f1 -f2, signal processing means for (a) producing from said fourth electrical signal a plurality of time segments such that each time segment of frequency 2f1 -f2 begins with the same phase, (b) averaging over a predetermined number of said time segments of said fourth electrical signal to produce an averaged signal, and (c) applying said averaged signal to a spectrum analyzer for determining the amplitude versus frequency spectrum of said averaged signal, whereby said amplitude at said frequency 2f1 -f2 substantially represents the level of said distortion product emission tone and the noise level at other frequencies is substantially reduced, said spectrum analyzer means including a trigger input and a signal input, wherein said first output lead is connected to said signal input of said spectrum analyzer and said third electrical square wave signal of frequency 2f1 -f2 is applied to said trigger input.
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11. A method for reducing noise in distortion product emission testing comprising the steps of:
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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, producing an averaged signal by averaging segments of said steady-state electrical signal which occur in said time samples; and applying said averaged signal to a Fourier-transform spectrum analyzer to determine the amplitude level of said DPE tone of said averaged signal, whereby noise is reduced. - View Dependent Claims (12, 13)
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Specification