Hearing Aid Beamformer for Sound Localization
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Solution Overview
Problem
Hearing aids with microphones placed behind the ear tend to emphasize sounds from behind the user over those from the front due to the shadowing effect of the head and ears, leading to impaired sound localization.
Innovation Solution
A method is implemented in hearing aids to determine complex, frequency-dependent constants for a beamformer filtering unit, combining signals from multiple microphones to optimize the directional response, mimicking the ideal microphone placement near the eardrum, thereby compensating for the inherent preference towards non-target directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If microphones are placed behind the ear in a BTE hearing aid, then the device can be worn comfortably and is easy to operate, but the microphones tend to over-emphasize signals from behind the user compared to frontal directions due to the shadowing effect of the head and ears
Solution Approach 1:
The patent applies parameter changes by modifying the frequency response characteristics of the microphone system through digital signal processing. Specifically, it adjusts the gain and phase parameters across different frequency bands to compensate for the shadowing effect, transforming the directional response pattern to achieve more accurate sound localization while maintaining the comfortable behind-the-ear placement
Solution Approach 2:
The patent introduces an intermediary element in the form of a transfer function that models the acoustic path from the microphone location behind the ear to the eardrum. This transfer function acts as a mediator that characterizes and compensates for the shadowing effect, allowing the system to predict and correct directional response errors without changing the physical microphone placement
2Ease of manufacture
If microphones are placed away from the ear canal (e.g., behind the ear), then the hearing aid structure is simpler and easier to manufacture, but the spatial properties of processed sound differ from the ideal properties at the eardrum
Solution Approach 1:
The patent creates a virtual copy of the ideal ear canal microphone response through signal processing. By measuring or modeling the transfer function from the behind-ear microphone location to the eardrum, the system synthesizes a signal that replicates what an ideal ear canal microphone would capture, thereby copying the desired spatial properties without requiring the physical microphone to be located at the ear canal
3Measurement precision
If the microphone location effect compensation is applied to correct frequency response from the target direction, then the frequency accuracy is improved, but the directional response from all other directions remains uncorrected
Solution Approach 1:
The patent segments the directional space into multiple regions (frontal direction, lateral directions, and rear directions) and applies different compensation strategies to each segment. By dividing the omnidirectional response correction into directional segments, the system can optimize the frequency response for the target direction while also improving the directional accuracy for sounds from other directions through the beamformer filtering unit
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances sound localization by minimizing the difference between the resulting transfer function of the microphones placed behind the ear and those ideally located in the ear canal, providing a more accurate directional response similar to that of microphones near the eardrum.
Implementation Method 1
first and second microphones for converting an input sound to first and second electric input signals
Implementation Method 2
a beamformer filtering unit for providing a beamformed signal Y as a weighted combination of said first and second electric input signals using said complex, frequency dependent constants
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
The application relates to a hearing aid comprising a BTE-part adapted for being located behind an ear (ear) of a user. The BTE-part comprises a) a multitude M of microphones (MBTEi, i=1, .., M) for converting an input sound to respective electric input signals (INi, i=1, ..., M), the multitude of microphones of the BTE-part, when located behind the ear of the user being characterized by transfer functions HBTEZ(θ, ϕ, r, k), i= 1, ..., M, representative of propagation of sound from sound sources S located at (θ, ϕ, r) around the hearing aid to the respective microphones (MBTEi, i=1, ..., M), when the BTE-part is located at its operational position, (θ, ϕ, r) representing spatial coordinates and k is a frequency index, b) a memory unit comprising complex, frequency dependent constants Wi(k)', i=1, ..., M, c) a beamformer filtering unit (BFU) for providing a beam formed signal Y as a weighted combination of said multitude of electric input signals using said complex, frequency dependent constants Wi(k)', i=1, ..., M,: Y(k)=W1(k)'·IN1+ ... +WM(k)'·INM, and wherein said frequency dependent constants Wi(k)', i=1, ..., M, are determined to provide a resulting transfer function Hpinnaθϕrk=∑i=1MWik⋅HBTEiθϕrk, so that a difference between the resulting transfer function Hpinna(θ, ϕ, r, k) and a transfer function HITE(θ, ϕ, r, k) of a microphone located close to or in the ear canal (ITE) fulfils a predefined criterion. The application further relates to a method of determining constants Wi', i=1, ..., M. The invention may e.g. be used in hearing instruments, headsets, ear phones, active ear protection systems, or combinations thereof.