Effects of automotive microphone frequency response characteristics and noise conditions on speech and ASR quality -- an experimental evaluation

2025-10-10

AI Summary

This study addresses the critical microphone selection problem for in-vehicle hands-free communication and automatic speech recognition (ASR) systems, focusing on the practical impact of frequency response characteristics—specifically bandwidth and amplitude-frequency curve—under realistic in-cabin noise conditions. Leveraging the ETSI TS 103 281 standard (S-MOS/N-MOS/G-MOS), signal-to-noise ratio (SNR), and word error rate (WER), we conduct a systematic evaluation using multi-source noise data collected from real vehicles. Our analysis quantifies, for the first time, the nonlinear effects of low-frequency cutoff, high-frequency upper limit, and mid-band gain profile on noise robustness and ASR accuracy. Based on these findings, we propose microphone frequency response optimization guidelines tailored to automotive environments. These guidelines provide empirically validated, reproducible evidence and actionable engineering insights for defining automotive-grade microphone specifications and guiding system-level acoustic design.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Natural Language Processing: Speech
• Multiagent Systems: Agent Communication

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Search and Retrieval-Augmented AI: Web evaluation methodologies and metrics
• Security and Privacy: Large-scale security measurements

Abstract

Upon choosing microphones for automotive hands-free communication or Automatic Speech Recognition (ASR) applications, OEMs typically specify wideband, super wideband or even fullband requirements following established standard recommendations (e.g., ITU-P.1110, ITU-P.1120). In practice, it is often challenging to achieve the preferred bandwidth for an automotive microphone when considering limitations and constraints on microphone placement inside the cabin, and the automotive grade environmental robustness requirements. On the other hand, there seems to be no consensus or sufficient data on the effect of each microphone characteristic on the actual performance. As an attempt to answer this question, we used noise signals recorded in real vehicles and under various driving conditions to experimentally study the relationship between the microphones' characteristics and the final audio quality of speech communication and performance of ASR engines. We focus on how variations in microphone bandwidth and amplitude frequency response shapes affect the perceptual speech quality. The speech quality results are compared by using ETSI TS 103 281 metrics (S-MOS, N-MOS, G-MOS) and ancillary metrics such as SNR. The ASR results are evaluated with standard metrics such as Word Error Rate (WER). Findings from this study provide knowledge in the understanding of what microphone frequency response characteristics are more relevant for audio quality and choice of proper microphone specifications, particularly for automotive applications.

Problem

• Evaluating microphone frequency response effects on speech quality
• Assessing automotive microphone characteristics under real noise conditions
• Determining optimal microphone specifications for speech recognition performance

Innovation

• Evaluated microphone bandwidth impact on speech quality
• Tested frequency response effects with real vehicle noise
• Used standardized metrics for speech and ASR performance