Minimum-Phase Hearing Aid Filtering for Low Delay Audio
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Solution Overview
Problem
Hearing aid systems face challenges in reducing processing delay while maintaining high frequency resolution, which affects sound quality, and existing methods to minimize delay require significant processing resources.
Innovation Solution
The method involves analyzing input signals to determine frequency-dependent target gains, calculating the real cepstrum, and using it to provide a desired minimum phase filter impulse response, with discrete cosine and sine transformations to optimize digital filter updates, reducing processing delay and improving sound processing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional filter banks are used to achieve high frequency resolution, then sound quality is improved, but processing delay increases
Solution Approach 1:
The patent changes the fundamental parameter of filter design by using minimum phase filters instead of traditional linear phase filters. This parameter change allows the system to achieve high frequency resolution while minimizing processing delay, as minimum phase filters have their energy concentrated as early as possible in the impulse response, thereby reducing the group delay across all frequencies.
Solution Approach 2:
The patent replaces the traditional mechanical approach of using long filter banks to achieve high resolution with a mathematical substitution approach. By computing minimum phase filters from magnitude responses using cepstral methods or other mathematical techniques, the system achieves the same frequency resolution without the temporal delay inherent in traditional filter designs.
2Loss of time
If processing delay is reduced using existing methods, then responsiveness is improved, but processing resources are significantly consumed
Solution Approach 1:
The patent segments the filter design process into two distinct stages: first computing the magnitude response based on hearing aid requirements, then deriving the minimum phase filter from this magnitude response. This segmentation allows the system to achieve low delay without requiring computationally intensive real-time optimization, as the minimum phase filter can be pre-computed or updated efficiently from the magnitude response.
Solution Approach 2:
The patent inverts the traditional filter design approach by starting with the magnitude response (frequency characteristics) and working backwards to derive the minimum phase filter, rather than designing filters directly in the time domain and then analyzing their frequency characteristics. This inversion allows for more efficient computation and reduced processing resources while maintaining low delay.
3Loss of time
If minimum phase filters are used to reduce processing delay, then responsiveness is improved, but frequency resolution may be compromised
Solution Approach 1:
The patent creates a composite filter design that combines the advantages of magnitude response control (for frequency resolution) with minimum phase characteristics (for low delay). By constructing filters that are minimum phase while maintaining the desired magnitude response, the system achieves both high frequency resolution and low processing delay simultaneously, rather than having to trade one off against the other.
Data Source
AI summary
A method of operating a hearing aid system comprising a hearing aid (300) wherein a digital filter (302) is adapted to be of minimum phase and to provide a frequency dependent target gain.