Virtual Sound Field Navigation via HOA Microphone Interpolation
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Solution Overview
Problem
Existing sound field navigation techniques either introduce spectral coloration or degrade sound quality when attempting to virtually navigate 2D or 3D sound fields, particularly when dealing with sound sources near microphone assemblies or in complex geometries.
Innovation Solution
The system employs an array of higher-order Ambisonics microphone assemblies to detect and locate near-field sound sources, then uses weighted averaging and linear translation filters to interpolate spherical harmonic coefficients from valid microphone assemblies to an intermediate listening position, ensuring accurate sound field reproduction without spectral degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If source separation technique is used in time-frequency domain, then sound sources can be isolated and moved, but sound quality degradation occurs
Solution Approach 1:
The patent uses spherical harmonic coefficients (SHCs) as an intermediary mathematical representation to describe the sound field, avoiding direct manipulation of individual sound sources. This mediator enables navigation by transforming the sound field representation rather than separating and moving discrete sources, thus preserving sound quality while achieving navigation capability.
Solution Approach 2:
The patent changes the parameter representation from time-frequency domain source separation to spherical harmonic domain field representation. By using SHCs to represent the sound field and applying spatial transformations in this parameter space, the system achieves navigation without the quality degradation associated with time-frequency separation techniques.
2Adaptability or versatility
If SHCs are averaged directly from multiple microphone assemblies, then navigation is achieved, but comb-filtering effect occurs when sources are nearer to one assembly
Solution Approach 1:
The patent applies local quality by selecting only those microphone assemblies whose valid spherical regions include the desired listening position. This selective approach ensures that each contributing microphone assembly has appropriate local coverage, avoiding the spectral distortion that would result from averaging SHCs from assemblies with overlapping but mismatched valid regions.
Solution Approach 2:
The patent segments the set of microphone assemblies into valid and invalid contributors based on geometric criteria. Only assemblies where the listening position falls within their valid spherical region are selected for interpolation, creating a segmented selection that prevents comb-filtering effects while maintaining navigation capability.
3Measurement precision
If SHCs from a single microphone assembly are used, then the sound field is accurately described, but only in a finite region around the assembly
Solution Approach 1:
The patent merges SHCs from multiple microphone assemblies through weighted interpolation to extend the spatial coverage beyond what a single assembly can provide. By combining data from multiple assemblies whose valid regions overlap or adjacent to the desired position, the system achieves both accuracy and extended spatial coverage.
Solution Approach 2:
The patent transitions from a single-point measurement (one microphone assembly) to a distributed multi-point measurement system. By utilizing SHCs from multiple assemblies positioned at different locations, the system effectively adds spatial dimensionality to the measurement, enabling accurate sound field description across a larger volume.
Data Source
AI summary
The system and method for virtual navigation of a sound field through interpolation of the signals from an array of microphone assemblies utilizes an array of two or more higher-order Ambisonics (HOA) microphone assemblies, which measure spherical harmonic coefficients (SHCs) of the sound field from spatially-distinct vantage points, to estimate the SHCs at an intermediate listening position. First, sound sources near to the microphone assemblies are detected and located. Simultaneously, the desired listening position is received. Only the microphone assemblies that are nearer to said desired listening position than to any near sources are considered valid for interpolation. The SHCs from these valid microphone assemblies are then interpolated using a combination of weighted averaging and linear translation filters. The result is an estimate of the SHCs that would have been captured by a HOA microphone assembly placed in the original sound field at the desired listening position.