Noise cancellation enabled audio system and method for adjusting a target transfer function of a noise cancellation enabled audio system
A noise cancellation enabled audio system for tonal tinnitus treatment using ambient noise comprises an audio processor (PROC) and at least one filter having an adjustable filter function. An ear mountable playback device (HP) further comprises a speaker (SP) and at least one feedforward microphone (FF_MIC). The audio processor (PROC) is configured to receive an input signal (Z(s)) from the feedforward microphone (FF_MIC) indicative of ambient noise and determine a filter transfer function (HF(s)) to realize a predetermined target transfer function (HT(s)), wherein the target transfer function (HT(s)) is configured to attenuate and/or amplify the input signal (Z(s)) in a predetermined frequency range. The filter function is adjusted depending on the filter transfer function (HF(s). The filter is configured to provide a system output signal (Y(s)) by filtering the input signal (Z(s)) depending on the filter function.
1. A noise cancellation enabled audio system for tonal tinnitus treatment using ambient noise, comprising:
an audio processor,
at least one filter having an adjustable filter function,
an ear mountable playback device further comprising a speaker and at least one feedforward microphone, and
an amplifier coupled between the audio processor and the speaker,
wherein the audio processor is configured to:
receive an input signal from the feedforward microphone indicative of ambient noise,
determine a filter transfer function to realize a predetermined target transfer function, wherein the target transfer function is configured to attenuate and/or amplify the input signal in a predetermined frequency range, and
adjusting the filter function depending on the filter transfer function; and
wherein the filter is configured to:
provide a system output signal by filtering the input signal depending on the filter function, and,
wherein:
the audio processor is provided with acoustic transfer functions between an ambient sound source creating the ambient noise and an eardrum exposed to the speaker, and
the audio processor is configured to determine the filter transfer function by compensating for the acoustic transfer functions, and
wherein the acoustic transfer functions comprise:
a first acoustic transfer function of the feedforward microphone, denoted H M (s),
a second acoustic transfer function of the amplifier, denoted H A (s),
a third acoustic transfer function of the speaker, denoted H S (s),
a fourth acoustic transfer function of the ear mountable playback device, denoted H H (s); and wherein:
the filter transfer function, denoted H F (s), is determined as
H
F
(
s
)
=
H
T
(
s
)
-
H
H
(
s
)
H
M
(
s
)
·
H
A
(
s
)
·
H
S
(
s
)
wherein HT(s) denotes the target transfer function.
2. The noise cancellation enabled audio system according to claim 1 , wherein:
the filter comprises at least one notch, and wherein
the predetermined target transfer function is configured to match a stop band of the notch to a tinnitus frequency to be provided to the audio processor.
3. The noise cancellation enabled audio system according to claim 1 , further comprising a feedback noise microphone located in proximity to the speaker, and wherein the fourth acoustic transfer function comprises a passive damping component due to the ear mountable playback device and an active damping component due to active noise cancellation by means of the feedback noise microphone.
4. The noise cancellation enabled audio system according to claim 1 , further comprising:
a control unit configured to store one or more predetermined target transfer functions; and wherein:
the audio processor comprises a first interface coupled to the control unit to receive the one or more predetermined target transfer functions from the control unit, and
the control unit comprises a second interface to set the one or more predetermined target transfer functions at the control unit.
5. The noise cancellation enabled audio system according to claim 4 , wherein the control unit comprises a wireless system-on-chip and the second interface is configured to set the one or more predetermined target transfer functions at the control unit by wireless communication.
6. The noise cancellation enabled audio system according to claim 1 , wherein the ear mountable playback device comprises several feedforward microphones connected to the audio processor via a beam forming unit for directional hearing.
7. The noise cancellation enabled audio system according to claim 1 , wherein the ear mountable playback device comprises a headphone or a hearing aid.
8. A method for adjusting a target transfer function of a noise cancellation enabled audio system comprising an audio processor and an ear mountable playback device further comprising a speaker and at least one feedforward microphone, the method comprising:
receiving using the feedforward microphone an input signal from a feedforward microphone, the input signal being indicative of ambient noise, and, using the audio processor:
determining a filter transfer function to realize a predetermined target transfer function, wherein the target transfer function is configured to attenuate and/or amplify the input signal in a predetermined frequency range,
adjusting a filter function of at least one filter of the noise cancellation enabled audio system depending on the filter transfer function,
providing acoustic transfer functions between an ambient sound source creating the ambient noise and an eardrum exposed to the speaker, and
determining the filter transfer function by compensating for the acoustic transfer functions, and
wherein the acoustic transfer functions comprise:
a first acoustic transfer function of the feedforward microphone, denoted H_M(s),
a second acoustic transfer function of an amplifier, denoted H_A(s),
a third acoustic transfer function of the speaker, denoted H_S(s),
a fourth acoustic transfer function of the ear mountable playback device, denoted H_H(s); and wherein:
the filter transfer function, denoted H_F(s), is determined as
H
F
(
s
)
=
H
T
(
s
)
-
H
H
(
s
)
H
M
(
s
)
·
H
A
(
s
)
·
H
S
(
s
)
wherein H_T(s) denotes the target transfer function.
9. The method according to claim 8 , wherein the fourth acoustic transfer function is provided with a passive damping component due to the ear mountable playback device and an active damping component due to active noise cancellation using the feedback noise microphone.
10. The method according to claim 8 , wherein the predetermined target transfer function is provided out of one or more predetermined target transfer functions by user interaction.
11. The method according to claim 10 , wherein the user interaction involves wireless communication of the one or more predetermined target transfer functions to the audio processor.