Open-Sphere Microphone Array Digital Beamforming
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Solution Overview
Problem
Open-sphere microphone arrays face dimensional challenges, particularly with directional microphones, where the gap between microphones becomes too small, affecting high-frequency directional performance, and existing solutions do not adequately address these issues.
Innovation Solution
A sound capture system employing an open-sphere microphone array with six omnidirectional microphones arranged around a point of symmetry, connected via an evaluation circuit that forms differential microphone constellations using digital signal processing, including sample and fractional delays to generate directional output signals, effectively creating unidirectional microphones without the need for bulky directional microphones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If microphones are moved closer to the center of the array to maintain directional performance at high frequencies, then directional performance is improved, but the gap between adjacent microphones becomes smaller causing them to touch
Solution Approach 1:
The patent replaces the mechanical arrangement of directional microphones with digital signal processing to achieve directional performance. Instead of physically positioning microphones to create directional patterns, the system uses omnidirectional microphones and applies digital beamforming techniques to synthesize directional response, thereby avoiding the mechanical constraint of microphone spacing.
Solution Approach 2:
The patent changes the operational parameters by using omnidirectional microphones (which have uniform sensitivity in all directions) instead of directional microphones, and compensates for the lack of inherent directionality through digital signal processing parameters such as delay times and weighting coefficients to achieve the desired directional patterns.
2Measurement precision
If directional microphones are employed to achieve directional sensitivity, then directional performance is improved, but the microphones become bulkier making array construction difficult
Solution Approach 1:
The patent substitutes the mechanical directional sensitivity provided by bulky directional microphones with a digital system that creates directional patterns through signal processing. Omnidirectional microphones with small capsules are used, and their outputs are processed digitally to achieve the same directional sensitivity that would otherwise require large physical structures.
Solution Approach 2:
The patent creates a virtual directional microphone by combining signals from multiple omnidirectional microphones through digital processing. Instead of using a single physical directional microphone with inherent directional properties, the system synthesizes directional response by copying and combining signals from multiple omnidirectional sources with appropriate delays and weightings.
3Ease of manufacture
If omnidirectional microphones are used in an open-sphere array, then array construction is simplified, but directional performance deteriorates without additional processing
Solution Approach 1:
The patent makes the microphone array dynamically steerable by using digital signal processing to change the directional patterns in real-time. The omnidirectional microphones remain fixed in position, but the system can dynamically adjust the beamforming weights and delays to steer the directional sensitivity in different directions, providing adaptability that compensates for the fixed physical arrangement.
Solution Approach 2:
The patent makes the omnidirectional microphones serve multiple functions: they simultaneously capture sound from all directions (omnidirectional capability) and, through digital processing, create directional patterns (directional capability). This multi-functionality allows the same simple microphone structure to achieve both ease of construction and directional performance.
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 configuration maintains directional performance up to high audio frequencies, providing accurate control over beampatterns in 3-D space and supporting applications like speech pickup, video conferencing, and sound field analysis without requiring expensive unidirectional microphones.
Implementation Method 1
The evaluation circuit employs digital signal processing under a sampling rate and comprises six subtraction nodes providing the six directional output signals
Implementation Method 2
Each first delaying path includes a sample delay that is a whole-number multiple of an inverse of the sample rate and a fractional delay that is not a whole-number multiple of the inverse of the sample rate
Data Source
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Figure 5~6
AI summary
A sound capture system comprises an open-sphere microphone array where at least four omnidirectional microphones providing at least four output signals are disposed around a point of symmetry and an evaluation circuit that is connected to the at least four microphones disposed around the point of symmetry and that is configured to superimpose the output signal of each pair of microphones disposed around the point of symmetry with the output signal of one of the other microphones and opposite each other in relation to the center of the sphere to form at least four differential microphone constellations providing at least four output signals, each differential microphone constellation having an axis along which it exhibits maximum sensitivity.