HRTF Processing to Reduce Comb Filtering in Spatial Audio

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Solution Overview

Problem

Comb filtering effects during spatial audio playback using headphones are more apparent when listeners are positioned symmetrically between virtual sound sources, causing degradation of the spatial audio reproduction, particularly affecting the perception of a virtual phantom center.

Innovation Solution

A system processes head-related transfer functions (HRTFs) to apply gains and phase shifts, adjusting the HRTF magnitude and phase to reduce comb filtering effects, maintaining spatial audio quality and localization accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If HRTF dataset is used for spatial audio playback, then spatial audio reproduction is achieved, but comb filtering effects occur causing degradation of audio quality

Engineering Contradiction:

Improvespatial audio reproductionVSAvoidcomb filtering effects

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The patent applies gain adjustments specifically in frequency ranges where comb filtering creates nulls (dips in frequency response). By boosting these frequencies, the harmful comb filtering effects are converted into beneficial compensation, resulting in a flatter overall frequency response and improved spatial audio quality.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent modifies the HRTF dataset by applying phase shifts and gain adjustments to alter the frequency and phase characteristics. These parameter changes compensate for comb filtering effects while preserving the spatial localization properties of the original HRTF data.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If phase shifts are applied to HRTFs to reduce comb filtering, then frequency response is improved, but sound level decreases

Engineering Contradiction:

Improvefrequency responseVSAvoidsound level

Core Design Contradiction:

Manufacturing precisionVSQuantity of substance

Solution Approach 1:

The patent applies gain adjustments in specific frequency ranges (e.g., 900 Hz to 1600 Hz) to compensate for the sound level reduction caused by phase shifts. This selective gain application restores the overall sound level while maintaining the improved frequency response characteristics.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If gain is applied to increase HRTF magnitude, then frequency response is enhanced, but localization accuracy may be affected

Engineering Contradiction:

Improvefrequency responseVSAvoidsound localization

Core Design Contradiction:

Manufacturing precisionVSMeasurement precision

Solution Approach 1:

The patent applies gain adjustments selectively in specific frequency ranges where comb filtering occurs, rather than applying uniform gain across all frequencies. This localized approach enhances frequency response in problematic areas while minimizing impact on the phase and timing cues essential for sound localization.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS12413922B1Method and system for processing head-related transfer functions

Publication Date: 2025.09.09 APPLE INC

AI summary

A method performed by a programmed processor of an audio system, the method includes retrieving a head-related transfer function (HRTF) dataset from memory, processing the HRTF dataset to remote comb filtering effects during audio playback; applying, to each HRTF in the processed HRTF dataset, a gain to increase a magnitude of the HRTF at a frequency range; and storing the processed HRTF dataset in memory.