Headphone Equalization Using Fit-Adaptive Playback Filtering
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Solution Overview
Problem
Headphones experience inconsistent audio playback due to variations in fit, leading to unintended bass response and a lack of faithful reproduction of the artist's intent, as the interaction between the headphone and the user's ear geometry affects sound leakage and the incident sound field.
Innovation Solution
An adaptive digital filter AEQ is added to the headphone system, which updates its transfer function on a per audio frame basis using an adaptive filter algorithm, cascaded with a fixed Media EQ to maintain a consistent sound profile across different fits and ear geometries, ensuring a desirable audio spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If headphones are designed with passive sound isolation, then sound leakage is reduced, but audio quality and fidelity become inconsistent due to variation in headphone fit
Solution Approach 1:
The system dynamically adapts the audio signal processing in real-time based on the actual transfer function measured during playback. The adaptive filter continuously adjusts equalization parameters to compensate for fit variations, transforming a static passive isolation design into a dynamic system that maintains consistent audio quality regardless of how the headphones fit the user's ear.
Solution Approach 2:
The system uses feedback from the internal microphone to measure the actual transfer function of the headphone-ear interface. This feedback loop enables the system to detect fit variations and automatically adjust the audio signal through adaptive equalization, closing the gap between the intended audio output and the actual perceived sound.
2Ease of operation
If headphones are designed for universal fit, then ease of use is improved, but audio fidelity deteriorates due to interaction with varying ear geometries
Solution Approach 1:
The system changes the parameters of the audio signal in real-time based on the measured transfer function. By continuously adapting equalization parameters to match the specific user's ear geometry and headphone fit, the system maintains high audio fidelity while preserving universal fit and ease of use.
3Reliability
If adaptive filtering is applied in real-time, then playback consistency is improved, but computational complexity increases
Solution Approach 1:
The system applies adaptive filtering selectively to specific frequency ranges and audio components where fit variations have the most impact. By focusing computational resources on the most critical aspects of audio reproduction rather than processing the entire spectrum uniformly, the system achieves playback consistency while managing computational complexity.
Data Source
AI summary
Automatic equalization for consistent headphone may take place in a playback mode of operation in which ANC is turned off and there is no direct feedback from an internal microphone (to the input of a speaker). An automatic user content equalization process is active during that mode of operation which adapts a filter AEQ to restore a flat or other desired frequency response at the output of the speaker despite variation in headphone fit. An estimate of a transfer function of a path S is determined, wherein the path S is from i) the input of the speaker of the headphone to the internal microphone signal. The filter AEQ is adapted based on the estimate of the transfer function of the path S while it filters user content audio that drives the input of the speaker of the headphone. Other embodiments are also described and claimed.