Hearing Signal Frequency Shifting Beyond the Nyquist Limit
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Solution Overview
Problem
Current digital hearing devices are limited by a sampling rate of 16 to 20 kHz, which restricts the audio bandwidth to 8 to 10 kHz, resulting in the loss of useful information above the Nyquist frequency, affecting sound localization and intelligibility of sharp consonants.
Innovation Solution
A method that involves converting the analog input signal to a first output signal with a final sampling rate and an intermediate signal with a higher sampling rate, applying band-pass filtering, and shifting the spectrum to a frequency range below the final sampling rate, allowing additional information above the Nyquist frequency to be processed, while reducing energy consumption through decimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If the sampling rate is increased to capture frequency information above the Nyquist frequency, then the usable audio bandwidth is improved, but the energy consumption increases proportionally
Solution Approach 1:
The patent segments the frequency spectrum into two parts: base-band information (below Nyquist frequency) and additional information (above Nyquist frequency). The base-band signal is processed at the normal lower sampling rate to conserve energy, while the additional high-frequency information is extracted and processed separately. This segmentation allows the system to utilize frequency information above the Nyquist frequency without proportionally increasing the overall processing speed and energy consumption.
Solution Approach 2:
The patent introduces an intermediary processing path for the high-frequency components. An intermediate signal is generated containing frequency information above the Nyquist frequency, which is then processed through separate algorithms before being combined with the base-band signal. This intermediary approach allows efficient handling of extended frequency range without requiring the entire system to operate at higher sampling rates.
2Loss of information
If the sampling rate is increased to 20 kHz or higher, then the audio bandwidth is extended, but the processing speed and energy consumption increase
Solution Approach 1:
The patent divides the signal processing into two independent streams: one processing base-band audio at the normal sampling rate (maintaining high processing speed for most audio content), and another processing the extended high-frequency components at the higher intermediate sampling rate. This segmentation ensures that the overall processing speed is not bottlenecked by the higher rate, as only a portion of the signal requires high-rate processing.
Solution Approach 2:
The patent applies partial high-rate processing only to the extent necessary for capturing and processing the extended frequency range. The intermediate signal processing algorithms operate at the higher sampling rate only when needed for frequency extension, while the majority of audio processing continues at the efficient lower sampling rate. This partial application of high-rate processing achieves the bandwidth extension goal without the full penalty of system-wide high-speed processing.
Data Source
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AI summary
The present invention is directed to a method and a hearing device for extending a usable frequency range of an analog input signal (i) being processed by a hearing device, the method comprising the steps of converting the analog input signal (i) to a first output signal (o1) and to an intermediate signal (om), the first output signal (o1) having a final sampling rate and the intermediate signal (om) having an intermediate sampling rate that is greater than the final sampling rate, applying a band-pass filter unit (31) to the intermediate signal (om) in order to obtain a filtered intermediate signal (omf), a lower cut-off frequency of the band-pass filter unit (31) being above half the final sampling rate, an upper cut-off frequency of the band-pass filter unit (31) being below half the intermediate sampling rate, and shifting a spectrum of the filtered intermediate signal (omf) to a frequency range being below the final sampling rate to obtain an intermediate output signal (om2).