Acoustic Sensor Calibration in Non-Anechoic Environments
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Solution Overview
Problem
Conferencing endpoints face challenges in calibrating multiple directional microphones due to variations in manufacturing tolerances and degradation over time, requiring assumptions about microphone directionality, speaker-to-microphone coupling, and room acoustics, which can corrupt the spatial capture of audio signals.
Innovation Solution
A calibration process that excites acoustic sensors with a stimulus in a non-anechoic environment, deriving a frequency-dependent calibration function by comparing the magnitude frequency response with a target response, allowing sensors to converge to a common frequency response without requiring knowledge of spatial relationships or room acoustics, and using techniques like deconvolution and windowing to prioritize diffuse-field data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods are used to calibrate multiple directional microphones, then the magnitude frequency response can be measured, but the spatial capture performance is corrupted due to direct-path dominance and assumptions about microphone directionality and speaker-to-microphone coupling
Solution Approach 1:
The patent extracts and removes the harmful direct-path contribution from the impulse response by identifying and eliminating the initial portion of the signal. This allows the calibration to proceed using only the diffuse-field portion of the impulse response, thereby preserving spatial capture performance while still achieving magnitude frequency response measurement.
Solution Approach 2:
The patent introduces an intermediary processing step that separates the impulse response into direct-path and diffuse-field components. By using this intermediary approach, the system can measure the magnitude frequency response without allowing the direct-path information to corrupt the spatial capture data.
2Ease of operation
If calibration is performed in a non-anechoic environment, then the calibration can be performed in practical conference rooms, but the direct-path signal dominates the measurement making it difficult to obtain accurate diffuse-field response
Solution Approach 1:
The patent extracts the diffuse-field portion from the total impulse response by removing the initial direct-path segment. This extraction technique enables accurate diffuse-field measurement in non-anechoic environments where the direct-path would otherwise dominate the signal.
Solution Approach 2:
The patent performs preliminary identification and removal of the direct-path contribution before proceeding with the calibration measurements. This preliminary action ensures that subsequent measurements are based solely on diffuse-field information, enabling accurate calibration in practical conference room environments.
3Manufacturing precision
If equalization is applied to uniformize microphone responses, then individual microphone variations are corrected, but the spatial characteristics and directional sensitivity of the microphone array are lost
Solution Approach 1:
The patent applies equalization only to the diffuse-field portion of the frequency response, leaving the spatial characteristics intact. By targeting only the non-spatial magnitude response for equalization, the system achieves microphone uniformity correction without compromising the directional sensitivity and spatial capture capabilities of the array.
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 enables effective calibration of acoustic sensors in a non-anechoic environment, preserving spatial capture and ensuring optimal performance by disregarding initial direct-path contributions and focusing on diffuse-field excitation, thus improving algorithmic performance and reducing measurement noise.
Implementation Method 1
Each acoustic sensor is excited by an acoustic stimulus travelling to the sensor as acoustic waves through the environment
Data Source
AI summary
A plurality of acoustic sensors in a non-anechoic environment are calibrated with the aim of removing manufacturing tolerances and degradation over time but preserving position-dependent differences between the sensors, The sensors are excited by an acoustic stimulus which has either time-dependent characteristics or finite duration. The calibration is to be based on diffuse-field excitation only, in which indirect propagation (including single or multiple reflections) dominate over any direct-path excitation. For this purpose, the calibration process considers only a non-initial portion of sensor outputs and/or of an impulse response derived there-from. Based on these data, a frequency-dependent magnitude response function is estimated and compared with a target response function, from which a calibration function is derived.