Multichannel Loudspeaker Calibration via Perceptual Reflection Filtering
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Solution Overview
Problem
Current sound reproduction calibration methods fail to optimally account for the temporal and spatial properties of sound reflections, leading to suboptimal listening quality in multichannel audio systems, as they focus solely on frequency correction without considering the impact of reflections on auditory perception and distribute processing effort inadequately across loudspeakers.
Innovation Solution
A method that obtains multidirectional impulse responses, analyzes them in a space-time domain to identify characteristics of direct and first reflections, compares reflection amplitudes to a perceptibility threshold, and modifies impulse responses to suppress non-perceptible reflections, determining a filtering matrix that minimizes error signals to enhance auditory perception by focusing processing on impactful reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If frequency equalization filtering is performed on each loudspeaker independently by inverting the measured impulse response, then the frequency response correction is improved, but the temporal and spatial information of reflections is lost
Solution Approach 1:
The patent segments the impulse response into distinct components: direct wave and reflections. By analyzing the impulse response in the time domain, the system identifies and separately processes the direct wave portion and the reflection portions, allowing frequency correction to be applied selectively without eliminating temporal information. This segmentation enables preserving reflection characteristics while achieving frequency response correction.
Solution Approach 2:
The patent transitions from traditional frequency-domain-only analysis to spatio-temporal domain analysis by incorporating spatial information (direction of incidence) and temporal information (time of arrival) dimensions. This multi-dimensional approach allows the system to characterize reflections by their spatial and temporal properties while performing frequency correction, thereby preserving information that would be lost in conventional monophonic frequency-domain methods.
2Device complexity
If correction filters are applied to each channel of the multi-channel signal individually, then the processing complexity is reduced, but the processing effort is not optimally distributed across loudspeakers
Solution Approach 1:
The patent merges the correction process across multiple loudspeakers by constructing a system matrix that incorporates impulse responses from all loudspeakers simultaneously. The multichannel inversion process solves for correction filters that consider the combined effect of all loudspeakers on the acoustic field, enabling optimal distribution of processing effort across the entire loudspeaker array rather than treating each channel in isolation.
Solution Approach 2:
The patent changes the approach from individual channel correction to system-wide correction by modifying the mathematical formulation to include cross-channel interactions. The system matrix formulation and multichannel inversion technique transform the problem from N independent single-channel corrections to one integrated multichannel correction process, optimizing the overall system performance while maintaining computational feasibility.
3Reliability
If all reflections are taken into account in the calibration process, then the completeness of the correction is improved, but processing instabilities and artefacts increase
Solution Approach 1:
The patent extracts and removes reflection components from the impulse response that fall below the perceptibility threshold. By identifying reflections through time-of-arrival and direction-of-incidence analysis, the system separates perceptible from non-perceptible reflections and excludes the latter from the correction calculation. This extraction process eliminates sources of processing instability and artifacts while maintaining correction accuracy for perceptible reflections.
Solution Approach 2:
The patent converts the potentially harmful effect of including all reflections (which causes processing instabilities) into a benefit by using the reflection characteristics (time of arrival, direction of incidence) to identify and exclude non-perceptible reflections. The very properties that make reflections problematic when all are included become the basis for selectively removing only those that would cause instability, while preserving perceptible ones.
Data Source
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AI summary
The invention relates to a method of calibrating a sound restitution assembly for a multichannel sound signal comprising a plurality of loudspeakers. The method comprises the steps of obtaining (E201) multidirectional impulse responses of the loudspeakers to the reproduction of a predetermined audio signal, of analyzing (E202) the multidirectional impulse responses obtained, in a domain of spatio-temporal representation, over at least one time window encompassing the instants of arrival of the first reflections of the predetermined audio signal reproduced so as to determine a set of characteristics (ARi, CRi, TRi) of the first reflections, of comparing (E203) the amplitude of each of the reflections with a predetermined perceptibility threshold (E204) and of identifying (E203) the imperceptible reflections for which the amplitude is below the predetermined threshold, of modifying (E205) the impulse responses obtained so as to obtain perceptive impulse responses, by deleting the reflections identified as imperceptible and of determining (E206) a filtering matrix on the basis of the perceptive impulse responses for an application of this filtering matrix to the multichannel audio signal before sound restitution. The invention also relates to a calibration device implementing the method described.