Open-Loop Audio Impulse Response Measurement for Microphone Arrays
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Solution Overview
Problem
It is challenging to accurately measure the characteristics of microphones integrated into speech-enabled devices like laptops and smartphones without direct access, as standard measurement techniques are distorted by device properties and signal processing.
Innovation Solution
An open-loop multichannel audio capture evaluation system that generates and analyzes test audio signals independently of the device, allowing for impulse response measurement, directional sensitivity estimation, and microphone geometry validation without synchronization or physical access to the microphones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If standard closed-loop measurement techniques are used to measure integrated microphones, then the measurement process is simplified, but the measurement precision deteriorates due to distortions from device properties and signal processing
Solution Approach 1:
The measurement system is segmented into independent components: an external audio signal generator separate from the device under test, and an analysis system that processes captured signals. This segmentation isolates the microphone measurement from device-related distortions, allowing accurate characterization of individual microphone properties without being affected by A/D converter quality or software stack processing
Solution Approach 2:
An external reference microphone and audio signal generator serve as intermediaries between the test environment and the integrated microphones. The reference microphone captures the original test signal, which then serves as a reference for comparing against signals captured by the integrated microphones, enabling accurate measurement while compensating for environmental and device-related variations
2Measurement precision
If microphones are accessed directly for measurement, then measurement precision improves, but device integrity and operational capability deteriorate
Solution Approach 1:
The measurement process extracts only the necessary audio signal information from the device without physically removing or altering the microphones. By using the device's existing audio capture path and processing the signals externally, the system obtains accurate microphone characteristics while leaving the microphones intact and fully functional within the device
Solution Approach 2:
The system creates a digital copy of the audio signals captured by the integrated microphones and processes this copy externally. By analyzing the captured signal copies rather than requiring direct physical access to the microphone elements, the system achieves measurement precision equivalent to direct access while maintaining complete device integrity
Data Source
AI summary
Techniques are provided for audio capture path evaluation of microphones incorporated into a device under test (DUT). A methodology implementing the techniques according to an embodiment includes estimating impulse responses (IRs) of the DUT microphones based on a comparison of a test audio signal received through the DUT microphones, at a selected measurement angle, to the test audio signal received through a reference microphone. The method also includes calculating group delays for the DUT microphones based on phase responses of the estimated IRs and calculating an average of the group delays. The method further includes calculating a distance, projected onto the measurement angle, between the DUT microphones and a geometric center of the DUT microphones. The distance is calculated as a product of the speed of sound and a difference between the average delay and the group delays for the DUT microphones. The process is repeated for additional measurement angles.