Adaptive Sample-Rate Conversion in Hearing Devices
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Solution Overview
Problem
Existing hearing devices face challenges in sample-rate conversion, leading to audible artefacts and variable latency due to buffer under-runs and over-runs, especially when input and processing rates diverge significantly, and current methods are inefficient in resource usage and adaptive control.
Innovation Solution
A method for adaptive sample-rate conversion that controls the conversion ratio based on estimated input-buffer levels, using upsampling and downsampling with dynamic selection of filter coefficients and subsets, minimizing artefacts and latency variations, and incorporating adaptive latency control to match reception quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simple skip-and-repeat sample-rate conversion is used, then the device complexity is reduced, but audible artefacts are generated in the processed signal
Solution Approach 1:
The patent segments the sample-rate conversion process into multiple stages: upsampling by a first factor, skip-and-repeat conversion, and downsampling by a second factor. This segmentation allows each stage to perform a specific function, with the upsampling stage preparing the signal for more accurate processing and the downsampling stage reducing the sample rate to the target rate, thereby reducing artefacts while managing complexity.
Solution Approach 2:
The patent implements dynamic control of the conversion ratio by adjusting the number of repeated samples based on buffer level monitoring. The system dynamically increases or decreases the conversion ratio when buffer under-run or over-run conditions are detected, allowing adaptive sample-rate conversion that maintains signal quality under varying input conditions.
2Stability of the object's composition
If upsampled skip-and-repeat method is used, then the processing rate can be maintained constant, but multiple skip or repeat operations occurring immediately after each other significantly reduce signal quality
Solution Approach 1:
The patent applies preliminary upsampling before the skip-and-repeat operation. By upsampling the input signal by a first factor before performing skip-and-repeat conversion, the system creates a more robust intermediate signal that reduces the impact of subsequent skip or repeat operations, thereby maintaining signal quality while achieving stable processing rate.
Solution Approach 2:
The patent implements feedback control by monitoring buffer levels and dynamically adjusting the conversion ratio. When buffer under-run or over-run conditions are detected, the system adjusts the number of repeated samples to maintain optimal signal quality, preventing multiple consecutive skip or repeat operations that would degrade the signal.
3Reliability
If retransmission of lost packets is implemented, then gaps in the processed audio signal are avoided, but the problems of multiple skip or repeat operations are worsened
Solution Approach 1:
The patent applies preliminary upsampling before the skip-and-repeat operation. By upsampling the input signal by a first factor before performing skip-and-repeat conversion, the system creates a more robust intermediate signal that reduces the impact of subsequent skip or repeat operations, thereby maintaining signal quality while achieving stable processing rate.
Solution Approach 2:
The patent implements dynamic control of the conversion ratio by adjusting the number of repeated samples based on buffer level monitoring. The system dynamically increases or decreases the conversion ratio when buffer under-run or over-run conditions are detected, allowing adaptive sample-rate conversion that maintains signal quality under varying input conditions.
4Speed
If the conversion ratio is changed immediately based on single sample information, then the response speed is increased, but multiple skip or repeat operations occur immediately after each other
Solution Approach 1:
The patent applies preliminary upsampling before the skip-and-repeat operation. By upsampling the input signal by a first factor before performing skip-and-repeat conversion, the system creates a more robust intermediate signal that reduces the impact of subsequent skip or repeat operations, thereby maintaining signal quality while achieving stable processing rate.
Solution Approach 2:
The patent implements feedback control by monitoring buffer levels and dynamically adjusting the conversion ratio. When buffer under-run or over-run conditions are detected, the system adjusts the number of repeated samples to maintain optimal signal quality, preventing multiple consecutive skip or repeat operations that would degrade the signal.
Data Source
AI summary
A hearing device comprises a receiver, an input buffer and a sample processor, the receiver being adapted to receive samples of a digital audio signal and feed received samples as a digital input signal to the input buffer, the sample processor being adapted to process the buffered samples to provide samples of a digital output signal such that the digital output signal is a sample-rate converted representation of the digital input signal with a predetermined target sample rate. The hearing device further comprises a latency controller adapted to estimate the quality of reception of the digital audio signal and to control the processing of the buffered samples in dependence on the estimated quality of reception.