Loudness compensation is used in audio systems to compensate for the human ear’s reduced sensitivity to low-level, low frequency sounds. Volume controls in both home and automotive audio systems feature bass boost to preserve the listening experience as volume is reduced.
Equal loudness contours from ISO226: 2003 suggest that at lower listening levels, as much as 30 dB of bass boost would be needed. In a vehicle, the essentially 1/F nature of cabin noise further suggests the need for bass content elevation. But loudness functions included in most vehicular systems today lack sufficient boost to meet either equal loudness requirements or vehicle noise compensation needs.
This paper discusses the history of loudness compensation, shows samples of loudness characteristics used today and discusses a limited experiment that attempted to examine the subject’s loudness compensation settings that they preferred during blind testing. These settings, and other observations of the author demonstrated an expected bass boosting and an unexpected, but similar amount of treble boosting.
Because of the ability of today’s audio DSP capability and the noise present in the automobile environment, the author recommends vehicle-specific tuning at multiple sound levels from which a loudness characteristic can be derived.