Parallel ANR and Hear-Through Signal Paths in Acoustic Devices
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Solution Overview
Problem
Active Noise Reduction (ANR) devices create acoustic isolation, which can be undesirable in certain situations, as they block ambient noise, preventing users from being aware of important sounds like announcements or allowing communication without removing the headphones.
Innovation Solution
Implementing an ANR signal flow path in parallel with a pass-through signal flow path, where the gain of the pass-through signal path is controllable by the user, allowing for adjustable ambient noise input without turning off or reducing ANR functionality, using a configurable digital signal processor and filter configurations like feedforward and feedback compensators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If ANR functionality is activated to block ambient noise, then noise reduction performance is improved, but user awareness of ambient sounds deteriorates
Solution Approach 1:
The audio signal is segmented into multiple frequency bands using a filter bank. Different processing is applied to different frequency segments: lower frequency bands undergo ANR processing while higher frequency bands are passed through with enhanced gain, allowing noise reduction in problematic frequencies while preserving awareness of important ambient sounds in other frequencies.
Solution Approach 2:
Different quality characteristics are applied to different parts of the audio spectrum. The ANR effect is applied locally to specific frequency ranges where noise blocking is most needed, while other frequency ranges maintain or enhance ambient sound transmission, creating non-uniform local qualities across the frequency domain.
2Loss of information
If hear-through mode is activated to allow ambient sounds, then ambient sound awareness is improved, but noise reduction performance deteriorates
Solution Approach 1:
The system dynamically adjusts the balance between ANR and hear-through modes by allowing continuous gain control of the pass-through signal path. Users can adjust the mix in real-time based on environmental conditions and personal preference, creating a dynamic rather than static operating state.
3Adaptability or versatility
If ANR and pass-through modes are switched separately, then functional flexibility is improved, but audible artifacts and user experience deteriorate
Solution Approach 1:
The ANR signal path and pass-through signal path are merged into a single parallel processing architecture. Both paths operate simultaneously with independently controllable gains, allowing seamless blending of noise reduction and ambient sound transmission without the abrupt transitions and artifacts associated with sequential mode switching.
4Loss of information
If pass-through gain is increased to hear ambient sounds, then ambient sound awareness is improved, but ANR effectiveness deteriorates
Solution Approach 1:
The system changes multiple parameters simultaneously: it applies frequency-dependent gain adjustments across different bands, modifies the ANR filter characteristics based on the pass-through gain setting, and adjusts the mixing ratio between processed and unprocessed signals. This multi-parameter adjustment maintains noise reduction effectiveness while allowing ambient sound awareness.
Data Source
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AI summary
Technology described in this document can be embodied in a method that includes receiving an input signal captured by one or more sensors associated with an active noise reduction (ANR) device, processing the input signal using a first filter disposed in an ANR signal flow path to generate a first signal for an acoustic transducer of the ANR device, and processing the input signal in a pass-through signal flow path disposed in parallel with the ANR signal flow path to generate a second signal for the acoustic transducer. The pass-through signal flow path is configured to allow at least a portion of the input signal to pass through to the acoustic transducer in accordance with a variable gain associated with the pass-through signal flow path. The method also includes generating an output signal for the acoustic transducer based on combining the first signal with the second signal.