Directional Microphone Equalization Using Omnidirectional Reference
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Solution Overview
Problem
Directional microphones in conferencing systems suffer from spectral peaks due to acoustic reflections, leading to an unpleasant 'boxy' artifact, while omnidirectional microphones pick up reverberation and noise from all directions, making them less desirable despite their lower sensitivity to reflections.
Innovation Solution
The spectral response of an omnidirectional microphone is used as a reference to develop scale factors for spectral equalization of directional microphones by decomposing their outputs into sub-bands and applying these scale factors to reduce the effects of acoustic reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If directional microphones are used to reduce reverberation and noise pickup, then directionality and noise rejection are improved, but spectral peaks and 'boxy' artifacts are introduced due to acoustic reflections
Solution Approach 1:
An omnidirectional microphone is introduced as an intermediary reference device to capture the room's acoustic characteristics without directional bias. Its output serves as a reference signal that mediates the equalization process, allowing the system to identify and compensate for spectral peaks in directional microphone signals caused by acoustic reflections
Solution Approach 2:
The system changes the spectral parameters of directional microphone signals by applying scale factors derived from comparing their frequency responses to the omnidirectional reference. This parameter adjustment equalizes the spectral content across different microphones, removing the boxy artifacts while preserving the directional noise rejection benefits
2Object-generated harmful factors
If omnidirectional microphones are used to avoid spectral peaks from acoustic reflections, then spectral flatness is improved, but reverberation and noise pickup from all directions increases
Solution Approach 1:
The omnidirectional microphone serves as a reference intermediary that captures pure spectral information without directional coloration. Rather than using its signal directly for conferencing, it mediates the equalization process by providing a baseline frequency response that guides the correction of directional microphone signals
Solution Approach 2:
The audio signal is segmented into frequency sub-bands for comparative analysis between omnidirectional and directional microphone outputs. This segmentation allows the system to identify specific spectral peaks in each band and apply targeted equalization, rather than treating the entire frequency spectrum uniformly
3Manufacturing precision
If spectral equalization using omnidirectional reference is applied to directional microphones, then audio quality and spectral flatness are improved, but system complexity increases
Solution Approach 1:
The system performs self-calibration by automatically comparing the frequency responses of omnidirectional and directional microphones and generating appropriate equalization parameters without manual intervention. This self-service approach simplifies deployment while maintaining high spectral equalization accuracy through automated scale factor calculation and application
Data Source
AI summary
The spectral response of an omnidirectional microphone is used as a reference. This reference is compared to the spectral response of each directional microphone to develop scale factors that are applied to the directional microphone spectral response to perform spectral equalization. The outputs of the omnidirectional microphone and the directional microphones are decomposed into a series of sub-bands and the comparison and equalization is done for each sub-band. The equalized sub-bands are then converted into a time domain signal for further processing by the conference phone or video conference system.