# US 8,542,855 B2 · System for reducing acoustic feedback in hearing aids using inter-aural signal transmission, method and use

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- Number: US 8,542,855 B2
- Document ID: US8542855B2
- Status: Granted
- Kind: B2
- Application number: 12/506,635
- Filed: 2009-07-21
- Published: 2010-01-28
- Granted: 2013-09-24
- Earliest claimed: 2008-07-24
- Assignees: Oticon A/S
- Applicants: Thomas Bo Elmedyb; Jesper Jensen; Meng Guo
- Inventors: Thomas Bo Elmedyb; Jesper Jensen; Meng Guo
- Web page: https://patentgrep.com/patent/US8542855B2

## CPC

- H04R 25/552: {Binaural}
- H04R 25/453: {electronically}
- H04R 5/033: Headphones for stereophonic communication {(details thereof, e.g. relating to batteries, cables or control elements H04R1/10)}
- H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K)

## Abstract

The invention relates to a hearing aid system comprising first and second spatially separated hearing instruments, the system being adapted for processing input sounds to output sounds according to a user's needs. The invention further relates to a method and use. The object of the present invention is to provide an alternative scheme for reducing the effect of acoustic feedback in a hearing aid system. The problem is solved in that the hearing instruments comprises, respectively, first and second input transducers for converting a first input sound to first and second electric input signal, and first and second output transducers for converting first and second processed electric output signal to first and second output sounds, wherein the system is adapted to provide that a first Tx-signal originating from the first electric input signal of the first hearing instrument is transmitted to the second hearing instrument and used in the formation of the second processed electric output signal, and that a second Tx-signal originating from the second electric input signal of the second hearing instrument is transmitted to the first hearing instrument and used in the formation of the first processed electric output signal. This has the advantage of providing a scheme for reducing or effectively eliminating acoustic feedback in a pair of hearing instruments. The invention may e.g. be used in listening devices, e.g. hearing aids, head sets, or active ear plugs.

## Claims

### Claim 1

A hearing aid system, comprising:
first and second spatially separated hearing instruments, the system being configured to process input sounds to output sounds according to a user's needs, the first hearing instrument including
a first input transducer for converting a first input sound to a first electric input signal;
a first output transducer for converting a first processed electric output signal to a first output sound; and
a first signal processing unit (SPU-1) configured
to process a first SPU-1-input signal,
to provide a first frequency dependent forward gain G-11, and
to provide a corresponding processed G-11-output signal; and
the second hearing instrument including
a second input transducer for converting a second input sound to a second electric input signal, and
a second output transducer for converting a second processed electric output signal to a second output sound,
the system being configured to provide that a first Tx-signal originating from the first electric input signal of the first hearing instrument is transmitted to the second hearing instrument and used in the formation of the second processed electric output signal,
that a second Tx-signal originating from the second electric input signal of the second hearing instrument is transmitted to the first hearing instrument and used in the formation of the first processed electric output signal,
to provide that the first SPU-1-input signal originates from the second Tx-signal, and
the system is configured to provide that the first processed electric output signal originates from the processed G-11-output signal.

### Claim 2 (depends on 1)

A hearing aid system according to claim 1, wherein
the first signal processing unit (SPU-1) is configured to process a second SPU-1-input signal, for providing a second frequency dependent forward gain G-12, and to provide a corresponding processed G-12-output signal, and
the system is configured to provide that the second SPU-1-input signal originates from the first electric input signal.

### Claim 3 (depends on 1)

A hearing aid system according to claim 1, wherein the system is configured to provide that the first Tx-signal is equal to the first electric input signal.

### Claim 4 (depends on 1)

A hearing aid system according to claim 1, wherein the second hearing instrument comprises a second signal processing unit (SPU-2) for processing a first SPU-2-input signal, providing a first frequency dependent forward gain G-21, and providing a corresponding processed G-21-output signal, and wherein the system is configured to provide that the first SPU-2-input signal originates from the first Tx-signal.

### Claim 5 (depends on 4)

A hearing aid system according to claim 4 wherein the second signal processing unit (SPU-2) is adapted for processing a second SPU-2-input signal, for providing a second frequency dependent forward gain G-22, and for providing a corresponding processed G-22-output signal, and wherein the system is adapted to provide that the second SPU-2-input signal originates from the second electric input signal.

### Claim 6 (depends on 5)

A hearing aid system according to claim 5, wherein
the system is configured to provide that the second processed electric output signal originates from a combination of the processed G-21-output signal and the processed G-22-output signal.

### Claim 7 (depends on 4)

A hearing aid system according to claim 4, wherein
the system is configured to provide that the second processed electric output signal originates from the processed G-21-output signal.

### Claim 8 (depends on 1)

A hearing instrument according to claim 1, wherein the signal processing unit (SPU-1, SPU-2) is configured to process the SPU-input signal(s) in the frequency domain in a number N of frequency bands FBi, the signal processing unit providing a forward gain Gi in each band, i=1, 2, . . . , N.

### Claim 9 (depends on 8)

A hearing aid system according to claim 8 configured to provide that loop gain is smaller than one in at least one of the frequency bands FBi considered by the system, i=1, 2, . . . , N, LGk(f)=|H1(f)·G2(f)·H2(f)·G1(f)|<1, for all frequencies fin the kth k frequency band.

### Claim 10 (depends on 8)

A hearing aid system according to claim 8 configured to determine the frequency band or bands that produce feedback oscillation.

### Claim 11 (depends on 10)

A hearing aid system according to claim 10 adapted to dynamically, with a certain frequency over time, determine the frequency band or bands most likely to produce feedback oscillation.

### Claim 12 (depends on 10)

A hearing aid system according to claim 10 configured to provide that LGq(f)=|H1(f)·G2(f)·H2(f)·G1(f)|<1, for all frequencies f in the frequency band or bands FBq detected to produce feedback oscillation.

### Claim 13 (depends on 8)

A hearing aid system according to claim 8 configured to, in advance of its use, determine the frequency band or bands that produce feedback oscillation.

### Claim 14 (depends on 8)

A hearing aid system according to claim 8 adapted to provide that the forward gains Gi1 and Gi2 of the frequency bands FBi1 and FBi2 of the first and second hearing instruments, respectively, are complementary to each other.

### Claim 15 (depends on 1)

A hearing aid system according to claim 1, configured to preserve directional cues of the input sound signals to the first and second hearing instruments.

### Claim 16

A hearing aid system, comprising:
first and second spatially separated hearing instruments, the system being configured to process input sounds to output sounds according to a user's needs, the first hearing instrument including
a first input transducer for converting a first input sound to a first electric input signal;
a first output transducer for converting a first processed electric output signal to a first output sound;
a first signal processing unit (SPU-1) configured
to process a first SPU-1-input signal, to provide a first frequency dependent forward gain G-11, and to provide a corresponding processed G-11-output signal, and
to process a second SPU-1-input signal, to provide a second frequency dependent forward gain G-12, and to provide a corresponding processed G-12-output signal; and
the second hearing instrument including
a second input transducer for converting a second input sound to a second electric input signal, and
a second output transducer for converting a second processed electric output signal to a second output sound,
the system being configured to provide that a first Tx-signal originating from the first electric input signal of the first hearing instrument is transmitted to the second hearing instrument and used in the formation of the second processed electric output signal,
that a second Tx-signal originating from the second electric input signal of the second hearing instrument is transmitted to the first hearing instrument and used in the formation of the first processed electric output signal,
to provide that the first SPU-1-input signal originates from the second Tx-signal,
to provide that the second SPU-1-input signal originates from the first electric input signal, and
the system is configured to provide that the first processed electric output signal originates from a combination of the processed G-11-output signal and the processed G-12-output signal.

### Claim 17

A hearing aid system, comprising:
first and second spatially separated hearing instruments, the system being configured to process input sounds to output sounds according to a user's needs, the first hearing instrument including
a first input transducer for converting a first input sound to a first electric input signal;
a first output transducer for converting a first processed electric output signal to a first output sound; and
a first signal processing unit (SPU-1) configured
to process a first SPU-1-input signal and a second SPU-1 input signal,
to provide a first frequency dependent forward gain G-11 and a second frequency dependent forward gain G-12, and
to provide a corresponding processed G-11-output signal and corresponding processed G-12-output signal; and
the second hearing instrument including
a second input transducer for converting a second input sound to a second electric input signal, and
a second output transducer for converting a second processed electric output signal to a second output sound,
the system being configured
to provide that a first Tx-signal originating from the first electric input signal of the first hearing instrument is transmitted to the second hearing instrument and used in the formation of the second processed electric output signal,
to provide that a second Tx-signal originating from the second electric input signal of the second hearing instrument is transmitted to the first hearing instrument and used in the formation of the first processed electric output signal,
to provide that the first SPU-1-input signal originates from the second Tx-signal,
to provide that the second SPU-1-input signal originates from the first electric input signal, and
wherein the system is configured to provide that the first Tx-signal originates from the processed G-12-output signal.

### Claim 18 (depends on 17)

A hearing aid system according to claim 17 wherein the system is adapted to provide that the second processed electric output signal is equal to the first Tx-signal.

### Claim 19

A hearing aid system, comprising:
first and second spatially separated hearing instruments, the system being configured to process input sounds to output sounds according to a user's needs, the first hearing instrument including
a first input transducer for converting a first input sound to a first electric input signal, and
a first output transducer for converting a first processed electric output signal to a first output sound,
the second hearing instrument including
a second input transducer for converting a second input sound to a second electric input signal, and
a second output transducer for converting a second processed electric output signal to a second output sound,
the system being configured
to provide that a first Tx-signal originating from the first electric input signal of the first hearing instrument is transmitted to the second hearing instrument and used in the formation of the second processed electric output signal,
to provide that a second Tx-signal originating from the second electric input signal of the second hearing instrument is transmitted to the first hearing instrument and used in the formation of the first processed electric output signal, and
to provide that loop gain is smaller than one, loop gain LG being given by LG=|H1·G2·H2·G1|<1, where Hn is the acoustic feedback transfer function and Gi is the forward transfer function of hearing instrument n, where n=1, 2.

### Claim 20 (depends on 19)

A hearing aid system according to claim 19 configured to provide that loop gain is smaller than one at all frequencies f considered by the system, LG(f)=|H1(f)·G2(f)·H2(f)·G1(f)|<1, for all frequencies in the frequency range, fmin≦f≦fmax, where fmin is 20 Hz and fmax is 12 kHz.

### Claim 21 (depends on 19)

A hearing aid system according to claim 19 adapted to provide that G1 and G2 are ‘complementary to each other’ in that |G1·G2|<1/|H1·H2|.

### Claim 22

A hearing aid system, comprising:
first and second spatially separated hearing instruments, the system being configured to process input sounds to output sounds according to a user's needs, the first hearing instrument including
a first input transducer for converting a first input sound to a first electric input signal, and
a first output transducer for converting a first processed electric output signal to a first output sound,
the second hearing instrument including
a second input transducer for converting a second input sound to a second electric input signal, and
a second output transducer for converting a second processed electric output signal to a second output sound,
the system being configured
to provide that a first Tx-signal originating from the first electric input signal of the first hearing instrument is transmitted to the second hearing instrument and used in the formation of the second processed electric output signal,
to provide that a second Tx-signal originating from the second electric input signal of the second hearing instrument is transmitted to the first hearing instrument and used in the formation of the first processed electric output signal,
to preserve directional cues of the input sound signals to the first and second hearing instruments, and
to utilize a prerecorded tabulation of the transfer functions from left-to-right and from right-to-left ear, HLR(ω,α) and HRL(ω,α), respectively, to preserve the directional cues of the input sound signals to the first and second hearing instruments.

### Claim 23 (depends on 22)

A hearing aid system according to claim 22 adapted to tabulate the acoustic feedback transfer functions HLR(ω,α) and/or HRL(ω,α) for different directions of arrival α of the target signal, where α is the angle of incidence of the target acoustic signal in the horizontal plane.

### Claim 24 (depends on 22)

A hearing aid system according to claim 22 adapted to tabulate the acoustic feedback transfer functions HLR(ω,φ) and/or HRL(ω,φ) for different directions of arrival φ of the target signal, where φ is the angle of elevation relative to a horizontal plane of the target acoustic signal.

### Claim 25 (depends on 22)

A hearing aid system according to claim 22 configured to compensate the directional cues by convolving the signal picked up from a given angle in the left ear with the impulse response corresponding to HLR(ω,α,φ), and vice-versa for the right ear.

### Claim 26

A hearing aid system, comprising:
first and second spatially separated hearing instruments, the system being configured to process input sounds to output sounds according to a user's needs, the first hearing instrument including
a first input transducer for converting a first input sound to a first electric input signal;
a first output transducer for converting a first processed electric output signal to a first output sound; and
a first signal processing unit (SPU-1) configured
to process a first SPU-1-input signal,
to provide a first frequency dependent forward gain G-11, and
to provide a corresponding processed G-11-output signal; and
the second hearing instrument including
a second input transducer for converting a second input sound to a second electric input signal, and
a second output transducer for converting a second processed electric output signal to a second output sound, wherein
the system is configured
to provide that a first Tx-signal originating from the first electric input signal of the first hearing instrument is transmitted to the second hearing instrument and used in the formation of the second processed electric output signal,
to provide that a second Tx-signal originating from the second electric input signal of the second hearing instrument is transmitted to the first hearing instrument and used in the formation of the first processed electric output signal, and
to provide that the first SPU-1-input signal originates from the second Tx-signal,
the signal processing unit (SPU-1, SPU-2) is configured to process the SPU-input signal(s) in frequency domain in a number N of frequency bands FBi, the signal processing unit providing a forward gain Gi in each band, i=1, 2, . . . , N, and
the system is further configured to provide that a sub-range SBi1j of a given frequency band FBi1 of the first hearing instrument is set to a relatively low value Glow,i1j of the forward gain and the corresponding sub-range SBi2j of the corresponding frequency band FBi2 of the second hearing instrument is set to a relatively high value Ghigh,i2j of the forward gain, and that a neighboring sub-range SBi1(j+1) of said frequency band FBi1 of the first hearing instrument is set to a relatively high value Ghigh,i1(j+1) and the corresponding sub-range SBi2(j+1) of the corresponding frequency band FBi2 of the second hearing instrument is set to a relatively low value Glow,i2(j+1), or vice versa.

### Claim 27

A hearing aid system, comprising:
first and second spatially separated hearing instruments, the system being configured to process input sounds to output sounds according to a user's needs, the first hearing instrument including
a first input transducer for converting a first input sound to a first electric input signal;
a first output transducer for converting a first processed electric output signal to a first output sound; and
a first signal processing unit (SPU-1) configured
to process a first SPU-1-input signal,
to provide a first frequency dependent forward gain G-11, and
to provide a corresponding processed G-11-output signal; and
the second hearing instrument including
a second input transducer for converting a second input sound to a second electric input signal, and
a second output transducer for converting a second processed electric output signal to a second output sound, wherein
the system is configured
to provide that a first Tx-signal originating from the first electric input signal of the first hearing instrument is transmitted to the second hearing instrument and used in the formation of the second processed electric output signal,
to provide that a second Tx-signal originating from the second electric input signal of the second hearing instrument is transmitted to the first hearing instrument and used in the formation of the first processed electric output signal,
to provide that the first SPU-1-input signal originates from the second Tx-signal,
the signal processing unit (SPU-1, SPU-2) is configured to process the SPU-input signal(s) in frequency domain in a number N of frequency bands FBi, the signal processing unit providing a forward gain Gi in each band, i=1, 2, . . . , N, and
frequency bands FBi1, FBi2 of the first and second hearing instruments each comprise two sub-bands, SBi11, SBi12 and SBi21, SBi22, respectively, each constituting half of the frequency range of that band.

### Claim 28

A hearing aid system, comprising:
first and second spatially separated hearing instruments, the system being configured to process input sounds to output sounds according to a user's needs, the first hearing instrument including
a first input transducer for converting a first input sound to a first electric input signal;
a first output transducer for converting a first processed electric output signal to a first output sound; and
a first signal processing unit (SPU-1) configured
to process a first SPU-1-input signal,
to provide a first frequency dependent forward gain G-11, and
to provide a corresponding processed G-11-output signal; and
the second hearing instrument including
a second input transducer for converting a second input sound to a second electric input signal, and
a second output transducer for converting a second processed electric output signal to a second output sound, wherein
the system is configured
to provide that a first Tx-signal originating from the first electric input signal of the first hearing instrument is transmitted to the second hearing instrument and used in the formation of the second processed electric output signal,
to provide that a second Tx-signal originating from the second electric input signal of the second hearing instrument is transmitted to the first hearing instrument and used in the formation of the first processed electric output signal,
to provide that the first SPU-1-input signal originates from the second Tx-signal,
the signal processing unit (SPU-1, SPU-2) is configured to process the SPU-input signal(s) in frequency domain in a number N of frequency bands FBi, the signal processing unit providing a forward gain Gi in each band, i=1, 2, . . . , N,
the system is configured to provide that at least some of the frequency bands FBi1, FBi2 of the first and second hearing instruments are arranged according to critical bands as defined by auditory perception theory, and
the system is configured to provide that the frequency bands FBi1, FBi2 are arranged to provide that a given desired signal power is present within each critical band while still avoiding feedback problems.

### Claim 29

A hearing aid system, comprising:
first and second spatially separated hearing instruments, the system being configured to process input sounds to output sounds according to a user's needs, the first hearing instrument including
a first input transducer for converting a first input sound to a first electric input signal;
a first output transducer for converting a first processed electric output signal to a first output sound; and
a first signal processing unit (SPU-1) configured
to process a first SPU-1-input signal,
to provide a first frequency dependent forward gain G-11, and
to provide a corresponding processed G-11-output signal; and
the second hearing instrument including
a second input transducer for converting a second input sound to a second electric input signal, and
a second output transducer for converting a second processed electric output signal to a second output sound, wherein
the system is configured
to provide that a first Tx-signal originating from the first electric input signal of the first hearing instrument is transmitted to the second hearing instrument and used in the formation of the second processed electric output signal,
to provide that a second Tx-signal originating from the second electric input signal of the second hearing instrument is transmitted to the first hearing instrument and used in the formation of the first processed electric output signal,
to provide that the first SPU-1-input signal originates from the second Tx-signal,
the signal processing unit (SPU-1, SPU-2) is configured to process the SPU-input signal(s) in frequency domain in a number N of frequency bands FBi, the signal processing unit providing a forward gain Gi in each band, i=1, 2, . . . , N,
the system is configured to provide that at least some of the frequency bands FBi1, FBi2 of the first and second hearing instruments are arranged according to critical bands as defined by auditory perception theory, and
the system is configured to provide that the frequency bands FBi1, FBi2 comprise both relatively high and relatively low gain values within each critical band.

### Claim 30

A method of reducing acoustic feedback in a hearing aid system comprising first and second hearing instruments, the system being configured to process input sounds to output sounds according to a user's needs, the method comprising:
converting an input sound to a first and a second electric input signal, respectively;
converting first and second processed electric output signals, respectively, to an output sound;
transmitting a first Tx-signal originating from the first electric input signal of the first hearing instrument to the second hearing instrument;
using the first Tx-signal in the formation of the second processed electric output signal;
transmitting a second Tx-signal originating from the second electric input signal of the second hearing instrument to the first hearing instrument;
using the second Tx-signal in the formation of the first processed electric output signal; and
setting loop gain to less than one, loop gain LG being given by LG=|H1·G2·H2·G1|<1, where Hn is the acoustic feedback transfer function and Gi is the forward transfer function of hearing instrument n, where n=1, 2.