Spectral Content Modification for Feedback Estimation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Feedback cancellation systems in hearing aids face challenges due to correlation between output and input signals, leading to signal distortions and reduced intelligibility, as traditional methods like probe noise techniques result in low 'probe noise-to-interference ratio' and long adaptation times.
Innovation Solution
The proposed solution involves spectral content modification using a model of the human auditory system to create an improved processed output signal that is less correlated with the input signal, employing techniques such as phase randomization and noise substitution, which allows for faster adaptation of the adaptive feedback cancellation filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If probe noise is added to the output signal to reduce autocorrelation, then the correlation between output and input signals is reduced, but the probe noise-to-interference ratio becomes very low and adaptation time increases
Solution Approach 1:
The patent modifies the spectral parameters of the output signal by applying frequency shifts and spectral transformations. This changes the correlation properties of the signal without adding external noise, thereby improving feedback cancellation accuracy while avoiding the low signal-to-noise ratio problems of probe noise methods
Solution Approach 2:
The patent introduces an intermediate signal processing stage that transforms the output signal through spectral modifications before it is used for feedback cancellation. This intermediary transformation creates sufficient decorrelation without requiring high levels of probe noise, thus avoiding the long adaptation times associated with low probe noise-to-interference ratios
2Reliability
If probe noise techniques are used to decorrelate output and input signals, then autocorrelation is reduced, but signal quality and intelligibility deteriorate due to low probe noise levels
Solution Approach 1:
The patent replaces the mechanical approach of adding physical probe noise with a signal processing approach using spectral transformations and frequency shifts. This substitution achieves the necessary signal decorrelation through mathematical operations rather than physical noise addition, maintaining signal quality while improving feedback cancellation accuracy
Solution Approach 2:
By applying frequency shifts and spectral transformations to the output signal, the patent changes the temporal and spectral parameters of the signal to reduce autocorrelation. This parameter modification achieves decorrelation without introducing low-level noise that would degrade signal quality and intelligibility
3Device complexity
If the output signal is used directly for feedback cancellation without modification, then the system is simple, but correlation between output and input signals causes signal distortions and loss of intelligibility
Solution Approach 1:
The patent segments the signal processing into distinct stages: original signal processing, spectral modification stage, and feedback cancellation stage. This segmentation allows the spectral modifications to be applied only to the portion of the signal used for feedback estimation, rather than to the entire audio output, thereby reducing overall system complexity while still achieving the necessary decorrelation to prevent signal distortions
Data Source
Figure 1
AI summary
The invention relates to a listening device for processing an input sound to an output sound according to a user's needs. The invention further relates to a method of reducing acoustic feedback in a listening device and to the use of a listening device. The object of the present invention is to provide an alternative scheme for feedback estimation in a listening device. The problem is solved in that the listening device comprises an input transducer for converting an input sound to an electric input signal, and an output transducer for converting a processed electric output signal to an output sound, a forward path being defined between the input transducer and the output transducer and comprising a signal processing unit adapted for processing an SPU-input signal originating from the electric input signal in a time-frequency representation comprising successive time frames each comprising a frequency spectrum of the signal in the time frame in question, the signal processing unit defining an input side and an output side of the forward path and comprising a spectral content modification unit adapted for modifying values of the signal of one or more regions of the frequency spectrum of a given time frame to provide that the modified values are less correlated to the corresponding time-frequency regions of the input signal than the unmodified output signal thereby providing an improved processed output signal, and a feedback loop from the output side to the input side comprising a feedback path estimation unit for estimating the effect of acoustic feedback from the output transducer to the input transducer, wherein the feedback path estimation unit is adapted to use the improved processed output signal in the estimation. This has the advantage of providing a better accuracy vs. tracking speed trade-off of the feedback path estimate. The invention may e.g. be used for listening devices prone to acoustic feedback, e.g. hearing aids, headsets or active earplugs.