Method and device for compensating for partial hearing loss

• US 4,868,880 A
• Filed: 06/01/1988
• Issued: 09/19/1989
• Est. Priority Date: 06/01/1988
• Status: Expired due to Term

• Current Assignee: Yale University
• Original Assignee: Yale University
• Inventors: Bennett, William R. Jr.
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US07/200,870
• Time in Patent Office: 475 Days
• Field of Search: 381/13, 381/98, 381/68.2, 381/68.4, 381/94, 381/103, 84/1.19, 84/DIG. 9
• US Class Current: 381/320
• CPC Class Codes: H04R 25/356 Amplitude, e.g. amplitude shift or compression
• CPC Class Codes: H04R 25/505 using digital signal processing

Abstract

A method and device for compensating for partial hearing loss by converting a time domain signal corresponding to a sound into a series of digital component values in the frequency domain, performing a nonlinear amplitude gain operation in the frequency domain on each of the digital component values and converting the digital component values back into a time domain signal corresponding to the sound with compensation for partial hearing loss.

Claims

1. A method of compensating for partial hearing loss, comprising the steps of:

a. converting a time domain signal corresponding to a sound into a series of digital component values in the frequency domain;

b. performing a non-linear amplitude gain operation in the frequency domain on each of the digital component values by determining a desired amplitude gain for each of a plurality of spectral component frequencies in the range of 20 to 20,000 Hz and performing the gain operation for each component value according to the desired gain for its corresponding frequency;

c. converting the digital component values from step (b) back into a time domain signal corresponding to the sound with compensation for partial hearing loss; and

d. wherein the desired amplitude gain for each frequency is determined according to exp (K), where the amplitude gain coefficient is

K=(y-y_o)Ln(10)/20 nepers

where y=T+(y_o -T_o) (P-T)/(P_o -T_o) dB

and y_o is the original sound intensity level in dB,

T is the threshold of hearing of a hearing impaired listener in dB,

T₀ is the normal threshold of heating in dB,

P is the threshold of pain for the hearing impaired listener in dB,

P₀ is the normal threshold of pain in dB, and

0 dB SIL reference level is 10^-16 Watts/cm².

2. The method according to claim 1, wherein step (a) comprises receiving a first analog signal corresponding to a sound to be heard, converting the first analog signal to a first digital time domain signal and performing a Fast Fourier Transform on the digital time domain signal to obtain a series of digitally represented frequency domain component values.

3. The method according to claim 2, wherein step (c) comprises performing an inverse Fast Fourier Transform to obtain a second digital time domain signal and converting the second digital signal to a second analog time domain signal.

4. The method according to claim 1, wherein step (b) includes the addition of a minimum-phase correction to each spectral component frequency after performing non-linear amplitude gain correction in the frequency domain on each of the digital component values.

5. The method according to claim 4, wherein the desired minimum phase correction φ

_o is determined according to ##EQU3## f_min is the minimum frequency for the hearing aid, f_max is the maximum frequency for hearing aid,

7. The method according to claim 1, wherein steps a-c are carried out in two channels in parallel for two ears.

9. The device according to claim 7, wherein the first means for converting comprises means for receiving a first analog signal corresponding to a sound to be heard, means for converting the first analog signal to a first digital time domain signal and means for performing a Fast Fourier Transform on the digital time domain signal to obtain a series of digitally represented frequency domain component values.

11. The device according to claim 7, wherein the second means for performing comprises means for storing a desired minimum phase correction for a plurality of component frequencies in the range of 20 to 20,000 Hz and means for performing the minimum phase correction for each component according to a desired minimum phase correction for the corresponding frequency.

13. The device according to claim 7, comprising two parallel channels, each channel having said first, second and third means therein and each channel associated with one of two ears.

6. π

=3. 14159 radians

K_o is the amplitude gain coefficient at frequency f_o in nepers.

8. A device for compensating for partial hearing loss, comprising:

a. first means for converting a time domain signal corresponding to a sound into a series of digital component values in the frequency domain;

b. second means for performing a non-linear amplitude gain operation in the frequency domain on each of the digital component values, comprising means for storing a desired amplitude gain for each of a plurality of component frequencies in t he range of 20 to 20,000 Hz and means for performing the gain operation for each component value according to the desired amplitude gain for its corresponding frequency;

c. third means for converting the digital component values from the performing means back into a time domain signal corresponding to the sound with compensation for partial hearing loss; and

d. means for determining the desired amplitude gain for each frequency according to exp (K), where the amplitude gain coefficient is

K=(y-y_o)Ln(10)/20 nepers

where y=T+(y_o -T_o)(P-T)/(P_o -T_o) dB

and y_o is the original sound intensity level in dB,

T is the threshold of hearing of a hearing impaired listener in dB,

T_o is the normal threshold of heating in dB,

P is the threshold of pain for the hearing impaired listener in dB,

P_o is the normal threshold of pain in dB, and OdB SIL reference level is 10^-16 Watts/cm².

10. The device according to claim 8, wherein the third means for converting comprises means for performing an inverse Fast Fourier Transform to obtain a second digital time domain signal and means for converting the second digital signal to a second analog time domain signal.

12. The device according to claim 10, further comprising means for determining the desired minimum-phase correction to each spectral component after performing the non-linear amplitude gain correction in the frequency domain, wherein the desired minimum phase correction φ

_o is determined according to ##EQU4## K_o is the amplitude gain coefficient at frequency f_o in nepers, f_min is the minimum frequency for the hearing aid,

f_max is the maximum frequency for hearing aid.