Planar Audio Tracking Using Virtual Microphone Arrays
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Solution Overview
Problem
Current audio tracking techniques are hindered by dominant reflections from surfaces like walls and tables, which negatively impact the accuracy of determining the audio source's bearing, especially when microphones are closely spaced.
Innovation Solution
A method and apparatus using at least three virtual cross-dipole microphones and a virtual monopole microphone for directional signal processing, filtering, and cross-correlating to estimate the angle of the dominant audio source, employing a filtered-sum beamformer to separate the audio source from reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If microphones are spaced closely together, then the device size is reduced and ease of installation is improved, but the ability to accurately determine bearing and separate audio source from reflections deteriorates
Solution Approach 1:
The patent combines signals from multiple microphones (including omnidirectional and directional microphones) to create virtual sensor arrays. By merging the outputs of closely spaced microphones through signal processing techniques like beamforming and cross-correlation, the system achieves bearing determination capability equivalent to widely spaced physical microphones, thus resolving the contradiction between compact size and measurement precision.
Solution Approach 2:
The patent transitions from spatial separation (physical distance between microphones) to signal processing dimension (virtual array construction). By creating virtual microphone arrays through mathematical operations on the signals from closely spaced physical microphones, the system achieves the bearing determination capability that would otherwise require physically distant microphones, effectively adding a processing dimension to overcome the spatial limitation.
2Reliability
If dominant reflections from walls and tables are present, then the audio environment becomes more realistic and complete, but the accuracy of audio source tracking deteriorates
Solution Approach 1:
The patent extracts the direct audio source signal from the mixed signal containing both direct sound and reflections.通过使用全向麦克风接收包含反射的混合信号，方向性麦克风接收主要直接声音，然后通过信号处理分离出直达声路径，将反射成分从直达声中提取出来并排除，从而解决了反射对定位精度干扰的问题。
Solution Approach 2:
The patent introduces cross-correlation as an intermediary tool to distinguish between direct sound and reflected sound. The cross-correlation function acts as a mediator that identifies the time delay and path differences between direct and reflected signals, allowing the system to selectively process only the direct sound path for bearing determination while maintaining awareness of the complete audio environment.
3Measurement precision
If widely spaced microphones are used, then bearing determination accuracy is improved, but device size increases and installation complexity increases
Solution Approach 1:
The patent creates virtual copies of microphone arrays through signal processing. Instead of physically deploying widely spaced microphones, the system processes signals from closely spaced microphones to create virtual sensor positions that mathematically replicate the response of widely spaced physical microphones. This copying approach achieves the same measurement precision without the physical complexity of large-scale deployment.
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
This approach effectively determines the angle of the dominant audio source even with closely spaced microphones, overcoming the limitations of dominant reflections and improving accuracy in audio tracking.
Implementation Method 1
cross-correlating means for cross-correlating the functions of the first cross-dipole and the monopole microphones and the functions of the second cross-dipole and the monopole microphones to produce respective estimates representative of the lag of the most dominant audio source
Data Source
AI summary
A planar audio tracking system comprises a square array of four microphones (M1, M2, M3, M4) arranged as first and second cross-dipole microphones and a virtually constructed monopole microphone. The signals from these microphones undergo directional pre-processing and the results are applied to a filtered sum beamformer (FSB) (32). The FSB identifies functions (hd (0), hd (π/2), and hm) of the FSB which are representative of impulse responses from desired audio source(s) to the first and second cross-dipole and the monopole microphone, respectively. The functions of the first cross-dipole and the monopole microphones and the functions of the second cross-dipole and the monopole microphones are cross correlated to produce respective estimates (ψc(l) and ψs(l)) representative of the lag of the most dominant audio source. An angle-estimate ({circumflex over (φ)}) of the most dominant source is determined using the estimates of lag. Other embodiments of the tracking system may comprise 3 microphones arranged in a circular array and forming first and second cross-dipoles and a virtual monopole.