Parallel Compensator Throttling for ANR Transducer Overload
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Solution Overview
Problem
Active noise reduction (ANR) devices face overload conditions due to low frequency pressure disturbances, leading to audible artifacts like oscillations and noise modulations, particularly in small form-factor devices like in-ear headphones, where the acoustic transducer is unable to handle the required displacement, resulting in objectionable user experiences.
Innovation Solution
Implementing a method that includes parallel processing of audio signals by first and second compensators, where the second compensator throttles the signal in the low frequency range upon detection of an overload condition, using a variable gain amplifier and tunable filters to adjust the signal flow path, thereby mitigating overload while maintaining noise reduction performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the acoustic transducer handles low frequency pressure disturbances with full compensation, then noise reduction performance is improved, but the transducer experiences overload conditions causing audible artifacts and reduced reliability
Solution Approach 1:
The system dynamically changes the compensation parameter (gain) based on signal frequency and overload detection. When overload is detected in the low frequency range, the compensator reduces gain selectively for frequencies below a threshold (e.g., 100 Hz), while maintaining full compensation for higher frequencies. This parameter adaptation prevents audible artifacts and transducer overload while preserving noise reduction effectiveness in the audible range.
Solution Approach 2:
The compensation is applied locally to specific frequency ranges rather than uniformly across all frequencies. The system identifies that low frequency disturbances (below threshold) cause overload and artifacts, while higher frequencies do not. Therefore, compensation is selectively applied: reduced or disabled for low frequencies causing problems, and maintained at full level for higher frequencies that contribute to audible noise reduction without causing overload.
2Reliability
If parallel compensators are used to process different frequency ranges, then overload conditions are mitigated, but device complexity increases
Solution Approach 1:
The signal processing is segmented into parallel paths: a first compensator processes the full frequency range, while a second compensator processes only the low frequency range (below threshold). This segmentation allows selective application of compensation strategies to different frequency bands, mitigating overload conditions in the low frequency range while maintaining simplicity through modular, parallel processing structures that can be efficiently implemented in digital signal processors.
3Duration of action of stationary object
If low frequency compensation is throttled to prevent overload, then transducer lifespan is extended, but noise reduction performance may be degraded
Solution Approach 1:
The system dynamically adjusts the compensation parameter (gain) based on detected overload conditions. When overload is detected, the gain for low frequency signals is reduced to protect the transducer and extend its lifespan. When no overload is present, full compensation is applied to maintain optimal noise reduction performance. This dynamic parameter adaptation ensures both transducer durability and performance effectiveness.
Data Source
AI summary
The technology described in this document can be embodied in a method that includes receiving an input signal representing audio captured by a microphone of an active noise reduction (ANR) headphone, and processing, by a first compensator, a first frequency range of the input signal to generate a first signal for an acoustic transducer of the ANR headphone. The method also includes processing, by a second compensator disposed in parallel to the first compensator, a second frequency range of the input signal to generate a second signal for the acoustic transducer. The first frequency range includes frequencies higher than the frequencies in the second frequency range. The method also includes detecting, by one or more processing devices, that the second signal satisfies a threshold condition, and attenuating the second signal responsive to determining that the second signal satisfies the threshold condition.