Hearing Device Sample Rate Conversion Latency Control
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Solution Overview
Problem
Existing hearing devices face challenges in sample-rate conversion, leading to audible artefacts and unpredictable latency due to variations in input and processing rates, and require efficient methods that minimize resource consumption and aliasing artefacts.
Innovation Solution
A method for controlling the conversion ratio by estimating average input-buffer levels and using upsampling and downsampling with polyphase filters, allowing for robust and efficient sample-rate conversion with precise latency control and minimal artefacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simple skip-and-repeat sample rate conversion is used, then device complexity is reduced, but audible artefacts increase and processing quality deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing conversion ratios for multiple input rate scenarios before runtime. The system determines appropriate conversion ratios in advance based on expected input rate ranges, and stores these pre-computed ratios in lookup tables. When rate conversion is needed, the system simply retrieves the pre-calculated ratio rather than computing it in real-time, thereby avoiding audible artefacts while keeping device complexity low.
Solution Approach 2:
The patent implements dynamics by making the conversion ratio adjustable and adaptive rather than fixed. The system dynamically selects from multiple pre-calculated conversion ratios based on the actual input rate conditions. This dynamic adaptation allows the system to optimize conversion quality for different operating conditions without requiring complex real-time computation, resolving the contradiction between simplicity and quality.
2Adaptability or versatility
If upsampling and downsampling with multiple operations are used to handle large rate variations, then adaptability to input rate variations improves, but device complexity and processing time increase
Solution Approach 1:
The patent applies partial action by using a single conversion ratio selection from pre-calculated options rather than performing multiple sequential upsampling and downsampling operations. The system pre-computes conversion ratios that can handle various input rate variations individually, and selects the appropriate one based on current conditions. This approach achieves the adaptability of handling large rate variations while avoiding the complexity of multiple conversion stages.
Solution Approach 2:
The system performs preliminary computation of conversion ratios for various input rate scenarios and stores them in advance. This pre-computation eliminates the need for complex real-time multi-stage conversion operations, allowing the system to adapt to different input rates by simply selecting from pre-prepared conversion parameters, thereby reducing device complexity while maintaining high adaptability.
3Reliability
If buffer size is increased to handle packet loss and retransmission, then reliability improves, but latency increases
Solution Approach 1:
The patent implements dynamics by making the buffer size adjustable rather than fixed. The system dynamically adapts the buffer size based on current network conditions, packet loss rates, and retransmission activity. When packet loss is detected or retransmission is occurring, the buffer size is temporarily increased to maintain reliability. When conditions are stable, the buffer size is reduced to minimize latency, thereby resolving the contradiction between reliability and latency.
Solution Approach 2:
The system periodically monitors buffer levels, packet arrival patterns, and retransmission activity to dynamically adjust buffer size. This periodic adaptation allows the system to maintain sufficient buffering during problematic periods (packet loss, retransmission) while minimizing buffering during stable periods, thereby achieving reliability when needed without permanently increasing latency.
4Speed
If conversion ratio changes are made immediately based on single sample information, then responsiveness to rate variations improves, but processing stability deteriorates due to multiple consecutive skips or repeats
Solution Approach 1:
The patent applies preliminary action by pre-calculating conversion ratios for various input rate conditions and storing them in lookup tables. When rate conversion is needed, the system retrieves the appropriate pre-computed ratio rather than making immediate changes based on single sample information. This pre-computation approach provides both responsiveness (by having pre-ready ratios for different conditions) and stability (by avoiding impulsive changes based on isolated samples).
Solution Approach 2:
The system uses feedback mechanisms to monitor input rate variations over time and adjust conversion ratio selection accordingly. By continuously monitoring the actual input rate and comparing it against expected ranges, the system can make informed decisions about which pre-calculated conversion ratio to use. This feedback-based approach prevents unstable behavior by ensuring conversion ratio changes are based on sustained rate variations rather than transient single-sample anomalies.
Data Source
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AI summary
In hearing devices, it is known to use sample-rate conversion to adapt the sampling rate of a received digital audio signal to the sample rate applied by the signal processing in the hearing device. The present invention aims to improve in particular the control of the latency caused by such sample-rate conversion. This is achieved in a hearing device (100, 200) comprising a receiver (101), an input buffer (102) and a sample processor (103), the receiver (101) being adapted to receive samples of a digital audio signal and feed received samples as a digital input signal (x(n)) to the input buffer (102), the sample processor (103) being adapted to process the buffered samples (x(n)) to provide samples of a digital output signal (y(m)) such that the digital output signal (y(m)) is a sample-rate converted representation of the digital input signal (x(n)) with a predetermined target sample rate (F y ), characterised in that the hearing device (100, 200) further comprises an estimator (104) adapted to estimate an average or smoothed input-buffer level (I(t)) indicating the number (N) of unprocessed samples (x(n)) in the input buffer (102) and a ratio controller (105) adapted to control the sample processor (103) in a manner aiming at minimising the difference (e(k)) between the estimated average or smoothed input-buffer level (I(t)) and a target buffer level (L). The invention allows for efficient and robust sample rate conversion with precise control of the latency, which depending on the implementation may be achieved at the cost of only minor artefacts in the processed signal.