Feed-Forward Acoustic Filtering for Ear-Coupled Volume Limiting
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Solution Overview
Problem
Electronic devices often exceed desirable acoustic output limits during ear-coupled listening due to high sound pressure levels, especially when combining audio sources and operational modes, leading to potential discomfort or missed alerts.
Innovation Solution
A feed-forward, filter-based acoustic control system that determines expected acoustic magnitudes for each frequency spectrum and attenuates specific frequencies to maintain output within safe limits while preserving overall audio quality and alert loudness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high sound pressure levels are used for audio playback, then audio output quality is improved, but acoustic comfort and safety deteriorate
Solution Approach 1:
The patent applies local quality by implementing frequency-dependent volume limiting. Different frequency bands are treated differently through separate gain stages and filters, allowing high sound pressure levels in safe frequency ranges while limiting levels in problematic frequencies (particularly low frequencies below 200Hz and high frequencies above 4kHz). This resolves the contradiction by maintaining high overall audio quality while locally suppressing harmful frequency components that cause acoustic discomfort.
Solution Approach 2:
The system dynamically changes acoustic parameters based on operational context. The volume limit threshold is adjusted according to device orientation (earpiece vs. loudspeaker mode), operational state (call vs. media playback), and detected frequency content. This allows the system to maintain high sound pressure levels when safe while automatically reducing levels when acoustic comfort becomes compromised, resolving the contradiction between audio quality and acoustic safety.
2Object-affected harmful factors
If volume is reduced for ear-coupled listening, then acoustic comfort is improved, but alert audibility deteriorates
Solution Approach 1:
The patent preserves alert audibility by applying local quality enhancement to alert frequencies. When an alert is detected, the system selectively boosts frequencies typical of alert sounds (mid-range frequencies around 1-4kHz where human speech and notification tones reside) while maintaining volume limits on problematic low and high frequencies. This resolves the contradiction by maintaining acoustic comfort through overall volume limiting while preserving alert detectability through frequency-selective enhancement.
Solution Approach 2:
The system performs preliminary detection of alert conditions before full volume limiting is applied. The alert detection mechanism identifies incoming calls, notifications, and other important alerts in advance, allowing the system to prepare appropriate frequency enhancement settings. This ensures that when alerts occur, they remain audible even though overall volume is limited for ear-coupled comfort, resolving the contradiction between comfort and alert audibility.
3Manufacturing precision
If frequency-dependent filtering is applied, then acoustic output control precision is improved, but device complexity increases
Solution Approach 1:
The patent implements segmentation by dividing the audio signal into multiple frequency bands (typically low, mid, and high frequencies) that are processed independently through separate gain stages and filters. Each band has its own volume control and limiting parameters, allowing precise acoustic output control for different frequency ranges. This segmentation approach achieves high control precision while managing complexity through modular, independent processing chains for each frequency band.
Solution Approach 2:
The system uses an intermediary feed-forward control mechanism that predicts and pre-limits excessive frequency components before they reach the output transducer. Rather than relying solely on feedback from microphones, the feed-forward path includes frequency-dependent filters and gain stages that proactively shape the audio signal. This intermediary processing achieves precise acoustic control while reducing the burden on feedback sensors and processing, managing overall system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively limits acoustic output to prevent discomfort while ensuring audible alerts and maintaining perceived loudness, enhancing user experience by dynamically adjusting volume based on operational contexts and hardware limitations.
Implementation Method 1
determining an expected acoustic magnitude respectively for each one of the more than one acoustic frequency spectra based on a predetermined acoustic conversion characteristic of the transducer(s) and based on the audio signal
Implementation Method 2
attenuating the first acoustic frequency spectrum to generate a filtered audio signal with an attenuated acoustic frequency spectrum that is less than or equal to the acoustic output threshold
Data Source
AI summary
An electronic device, method, and computer program product provide acoustic limiting of an audio output using a feed-forward, filter-based, acoustic control system. An audio signal is received that has more than one acoustic frequency spectra intended for conversion to an acoustic output by transducers of an electronic device. A determination is made of an expected acoustic magnitude respectively for each acoustic frequency spectrum of the more than one acoustic frequency spectra. A determination is made whether the expected acoustic magnitude of any acoustic frequency spectra will exceed an acoustic output threshold. The acoustic control system attenuates the first acoustic frequency spectrum to generate a filtered audio signal with an attenuated acoustic frequency spectrum that is less than or equal to the acoustic output threshold. The filtered audio signal is transmitted to the at least one transducer to the produce the audio output that does not exceed.