Method and device for continuous in-ear hearing health monitoring on a human being
A device and method for the continuous monitoring of otoacoustic emissions (OAE) levels on an individual worker uses as a pair of earpieces each featuring an external microphone, an internal microphone and a pair of miniature receivers. An adaptive filtering noise rejection processing of the measured distortion product OAE (DPOAE) is used to further improve the Signal-to-Noise ratio in frequencies where passive isolation remains insufficient. The adaptive filtering noise rejection technique relies on a Normalized Least-Mean-Square (NLMS) algorithm that uses the ipsilateral external microphone and the contralateral internal microphone to reject the noise from the measured DPOAE signals for each in-ear OAE probe. A DPOAE signal extraction algorithm provides for an increase in results reliability on a greater dynamic range in DPOAE magnitudes than known methods of DPOAE signal extraction. The device and method is suitable for the continuous monitoring of workers' hearing capabilities in industrial noises up to 75 dB(A).
1. A signal amplitude extraction method for providing a magnitude of a pre-filtered signal (s(n)) of a distortion product otoacoustic emission (DPOAE) for a continuous in-ear hearing health monitoring on a human being, the method comprising the steps of:
acquiring the DPOAE signal (s(n)) having a DPOAE frequency (f dp );
generating a carrier signal (c(n)) having a carrier frequency (f c ) generally equal to the DPOAE frequency (f dp );
normalizing the carrier signal (c(n)) with amplitude and phase tracking of the DPOAE signal (s(n)) to obtain a normalized modulating carrier signal (c 1 ′(n));
temporally modulating the DPOAE signal (s(n)) with the normalized modulating carrier signal (c 1 ′(n)) to set a constant magnitude modulated DPOAE signal (m 1 (n)); and
providing the constant magnitude modulated DPOAE signal (m 1 (n)) as a DPOAE magnitude output signal.
2. The method of claim 1 , wherein, for providing a magnitude of a noise signal around a frequency of the DPOAE signal (s(n)), the method further including the steps of:
transposing the carrier signal (c(n)) in frequency, by a frequency step, to obtain a frequency transposed carrier signal (c 2 ′(n));
temporally modulating the DPOAE signal (s(n)) with the frequency transposed carrier signal (c 2 ′(n)) to get the magnitude of the noise signal (m 2 (n)) around the DPOAE signal (s(n)); and
providing the magnitude of the noise signal (m 2 (n)) as a noise output signal.
3. The method of claim 2 , further including a step of averaging at least one of the magnitude of the noise signal (m 2 (n)) and the constant magnitude modulated DPOAE signal (m 1 (n)) with a running Root-Mean-Square (RMS) algorithm.
4. The method of claim 2 , wherein the frequency step varies from about 5 Hz to about 100 Hz.
5. The method of claim 3 , wherein the step of averaging converges within about 0.2 second.
6. The method of claim 1 , wherein the constant magnitude modulated DPOAE signal (m 1 (n)) is a 0-5 Hz signal (m 1 (n)).
7. The method of claim 1 , wherein the pre-filtered DPOAE signal (s(n)) is being pre-filtered with a noise rejection adaptive filter.
8. The method of claim 7 , wherein the noise rejection adaptive filter includes inner-ear and outer-ear adaptive filters.