Spectral Coherence Compensation for Stable Spatial Sound Fields
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Solution Overview
Problem
Existing sound field processing systems using stereo and multichannel microphone configurations often lose spatial information due to noise suppression processes, resulting in a mono output signal with no spatial information.
Innovation Solution
A system and method that calculates balance gains for multiple microphone signals, adjusts signal gains based on background noise estimates and echo cancellation processes, and blends signals to maintain spatial stability, using techniques like pair-wise spectral coherence to prevent high-frequency attenuation and enhance low-frequency signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If noise suppression processes are applied to multiple microphone signals, then noise performance is improved, but spatial information is lost resulting in mono output
Solution Approach 1:
The patent segments the noise suppression process by applying it independently to each microphone signal channel rather than mixing channels first. This allows noise reduction to be applied to individual channels while preserving the spatial relationships between channels, preventing the loss of spatial information that would occur with traditional mono processing.
Solution Approach 2:
The patent maintains the multi-dimensional spatial structure of the sound field by processing signals in the spatial domain rather than reducing to a single dimension. By calculating balance gains for each microphone signal and applying spectral coherence compensation across frequency bins, the system preserves the spatial dimensionality that would otherwise be lost in mono output.
2Object-generated harmful factors
If signal gains are adjusted for noise reduction, then noise artifacts are reduced, but high-frequency signals may be unnecessarily attenuated
Solution Approach 1:
The patent dynamically adjusts signal gains based on spectral coherence calculations that vary with frequency. By computing balance gains that are frequency-dependent rather than applying a uniform gain across all frequencies, the system can selectively attenuate noise in certain frequency ranges while preserving high-frequency signals that exhibit coherent spectral characteristics across microphone channels.
Solution Approach 2:
The patent uses spectral coherence as a feedback mechanism to monitor the relationship between microphone signals across frequency bins. This feedback information guides the adjustment of balance gains, allowing the system to distinguish between correlated signals (desired audio) and uncorrelated noise, thereby preventing unnecessary attenuation of genuine high-frequency content while still reducing noise artifacts.
3Stability of the object's composition
If balance gains are calculated for each microphone signal, then spatial stability is maintained, but device complexity increases
Solution Approach 1:
The patent changes the parameters used for spatial stability from complex multi-dimensional spatial coordinates to simplified balance gain ratios. By representing spatial relationships through gain adjustments rather than full spatial transformation matrices, the system maintains spatial stability while reducing computational complexity. The balance gain for each microphone signal serves as a compact parameter that encapsulates spatial positioning information.
Data Source
AI summary
In a system and method for maintaining the spatial stability of a sound field a balance gain may be calculated for two or more microphone signals. The balance gain may be associated with a spatial image in the sound field. Signal values may be calculated for each of the microphone. The signal values may be signal estimates or signal gains calculated to improve a characteristic of the microphone signals. The differences between the signal values associated with each microphone signal may be limited although some difference between signal values may be allowable. One or more microphone signals are adjusted responsive to the two or more balance gains and the signal gains to maintain the spatial stability of the sound field. The adjustments of one or more microphone signals may include mixing of two or more microphone. The signal gains are applied to the two or more microphone signals.