Headphone Transparency Filters for Natural Spatial Ambient Sound
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Solution Overview
Problem
Existing headphones attenuate ambient sound, making it difficult for users to hear their surroundings clearly, and existing transparency functions often distort the spatial cues and timbre of the ambient sound.
Innovation Solution
A headset system with exterior microphone arrays and digital processing to electronically reproduce ambient sound through earpiece speakers, using adaptive and non-adaptive filters to preserve spatial cues and timbre while reducing acoustic occlusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If headphones are designed to passively attenuate ambient sound, then noise isolation is improved, but acoustic transparency deteriorates
Solution Approach 1:
The patent replaces passive mechanical sound attenuation with active electronic sound reproduction. Exterior microphones capture ambient sound, digital signal processing filters and enhances the captured audio, and earpiece speakers reproduce the ambient sound electronically, substituting mechanical isolation with an electronic transparency system.
Solution Approach 2:
The patent introduces exterior microphones and digital processing as intermediaries between the ambient environment and the user's ear. The microphones capture sound that would otherwise be blocked by the headphone seal, and the processing system reconstructs the ambient sound field, mediating the interaction between the isolated ear and external environment.
2Loss of information
If transparency function reproduces ambient sound through speaker drivers, then ambient sound clarity is improved, but spatial cues and timbre are distorted
Solution Approach 1:
The patent applies digital signal processing to modify parameters of the captured ambient sound signal. Frequency-dependent filtering adjusts different frequency bands to compensate for the headphone's acoustic occlusion effects, and spatial processing algorithms adjust the stereo image and timing parameters to preserve spatial cues while enhancing overall clarity.
Solution Approach 2:
The patent creates a processed copy of the ambient sound field captured by exterior microphones. Rather than directly playing back the raw microphone signals, the system generates a transformed copy that compensates for occlusion effects and preserves spatial information, aiming to recreate the natural acoustic environment at the user's ear.
3Loss of information
If digital filters are applied to reduce acoustic occlusion, then ambient sound naturalness is improved, but device complexity increases
Solution Approach 1:
The patent performs preliminary measurements and characterizations of the headphone's acoustic occlusion effects during manufacturing. Transfer functions and filter coefficients are pre-computed based on these measurements, allowing the complex digital filtering to be implemented as relatively simple, pre-configured digital signal processing in the playback mode.
Solution Approach 2:
The system uses the headphone's own exterior microphones to capture and process the ambient sound that the headphone blocks. The digital processing system automatically adapts to the specific acoustic characteristics of each headphone unit through built-in calibration routines, making the complex processing self-adjusting rather than requiring external configuration.
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
The system allows users to hear ambient sound clearly and naturally, preserving spatial imaging and timbre, with adaptive filters providing customizable transparency modes.
Implementation Method 1
a left exterior microphone array and a right exterior microphone array
Implementation Method 2
plays it through the earpiece speaker drivers
Data Source
AI summary
Digital audio signal processing techniques used to provide an acoustic transparency function in a pair of headphones. A number of transparency filters can be computed at once, using optimization techniques or using a closed form solution, which are based on multiple re-seatings of the headphones and that are as a result robust for a population of wearers. In another embodiment, a transparency hearing filter of a headphone is computed by an adaptive system that takes into consideration the changing acoustic to electrical path between an earpiece speaker and an interior microphone of that headphone while worn by a user. Other embodiments are also described and claimed.