Standardized measurement of in-car audio systems remains an ongoing challenge, particularly regarding microphone configuration and placement, test signals, and correlation with perception. Current recommendations from the AES Technical Committee on Automotive Audio (TC-AA) advocate spatial averaging using multi-microphone arrays to improve repeatability. While this method reduces the influence of reflections and standing waves to improve frequency magnitude measurement consistency, it limits frequency, phase and amplitude resolution, which help identify the root causes of the distortions and evaluate their perceptual impact. An alternative approach is to apply frequency-normalized distortion analysis, where reflections or standing waves in the frequency response are also echoed in the distortion results, and eliminated by direct comparison of the two measurements. In this paper, spatial averaged distortion measurements using the TC-AA recommended 6 microphone array are compared with normalized distortion calculations, and a single microphone capture using the normalized distortion method. BSR measurements are also challenging. The TC-AA recommends a crest factor algorithm, available in most audio measurement systems. This adequately detects transient distortions, but is susceptible to background noise, therefore requires a tightly controlled environment for making measurements. Two other methods, enhanced perceptual Rub & Buzz and enhanced Loose Particles offer improved repeatability in the presence of background noise, and the results are easier to correlate to audibility. The three methods are compared, both in a quiet environment, and with background noise.
