Automotive OEMs invest significantly in branded audio systems to create differentiated, premium in-vehicle experiences. However, loudness tuning—critical for maintaining consistent perceived sound quality across listening levels—is often underdeveloped or inconsistently implemented. As a result, systems optimized at a single reference level can sound thin, unbalanced, or inconsistent under real-world usage conditions, negatively impacting perceived quality and brand identity. This paper presents a practical and production-ready methodology for loudness tuning based on ISO equal-loudness contours. Starting from a calibrated reference listening level, level-dependent compensation curves are derived to address changes in human auditory sensitivity at reduced playback levels. These compensations are implemented using a small set of efficient filters controlled via a volume-dependent lookup table, enabling scalable integration into automotive audio platforms. To further validate the approach, a benchmark dataset of over 200 production vehicles was analyzed, combining objective measurements with listener preference rankings. High-performing systems were used to derive effective loudness compensation characteristics, which shows a good alignment with ISO-based predictions while revealing systematic deviations due to in-cabin acoustics and playback conditions. The results demonstrate improved spectral consistency and preservation of brand sound signature, providing a high-impact, low-cost opportunity for OEMs to enhance perceived audio quality across all listening conditions.
