Hearing Aid Frequency Compression Harmonic Grid Restoration
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Solution Overview
Problem
Existing frequency compression methods in hearing aids disrupt the harmonic grid of audio signals, leading to perceivable artefacts, especially with voiced sounds, as they do not account for the line-like structure of harmonic signals, resulting in spectral lines no longer occurring at integer multiples of the fundamental frequency.
Innovation Solution
A method that includes harmonic correction during or after shifting, ensuring the harmonic is positioned as an integer multiple of the fundamental frequency, and further shifting is done in two steps: complete frequency channel shifting followed by amplitude modulation to restore the harmonic grid, using techniques like exp(j ω t) for accurate positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If frequency compression is performed by simply copying channels, then implementation is simple, but harmonic structure is disrupted causing perceptible artefacts
Solution Approach 1:
The patent applies preliminary action by estimating the fundamental frequency and identifying harmonic positions before the frequency compression is performed. This allows the system to pre-calculate target frequencies for harmonics and apply appropriate frequency shifts to maintain the harmonic grid structure, preventing artefact generation before it occurs.
Solution Approach 2:
The patent changes the frequency parameter of spectral components dynamically based on their relationship to the fundamental frequency. By calculating the distance of each harmonic from the fundamental frequency and applying proportional shifts, the system maintains the integer multiple relationships in the compressed spectrum, thereby preserving harmonic structure while achieving frequency compression.
2Reliability
If frequency compression shifts harmonics into target frequency range, then audibility is improved, but harmonic grid structure is destroyed
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the frequency shift amount for each harmonic based on its relationship to the fundamental frequency. The system calculates the distance of each harmonic from the fundamental frequency and applies a proportional shift, ensuring that the integer multiple relationships are preserved in the target frequency range, thereby maintaining both audibility and harmonic grid structure.
Solution Approach 2:
The patent employs feedback by continuously monitoring the spectral structure to identify the fundamental frequency and harmonic positions. This information feeds back into the frequency compression process, allowing the system to adaptively adjust frequency shifts to maintain harmonic relationships, ensuring that the compressed signal retains its natural harmonic structure.
3Productivity
If spectral lines are shifted without harmonic correction, then frequency compression is achieved, but spectral fine structure is degraded
Solution Approach 1:
The patent applies preliminary action by performing spectral analysis to identify the fundamental frequency and harmonic positions before frequency compression. This preliminary step allows the system to pre-calculate the appropriate frequency shifts needed to maintain harmonic relationships, enabling efficient compression while preserving spectral fine structure.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the frequency shift parameter for each spectral component based on its harmonic relationship to the fundamental frequency. This ensures that spectral lines are shifted to appropriate positions in the target frequency range while maintaining the integer multiple relationships that define the spectral fine structure.
Data Source
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AI summary
The method involves providing the audio signal into several frequency channels (31,32). The frequency associated with the fundamental frequency, in the frequency channel (32) is estimated as harmonic (20,30). The harmonics of the audio signal is moved or mapped from a frequency channel (31) in frequency channel (32). An independent claim is included for device for frequency compression of audio signal.