Application of the Composite Rating of Preference to Road and Wind Noise

The Composite Rating of Preference (CRP) was developed as an index to account for spectral balance and high frequency noise levels, in addition to the overall vehicle noise level, in subjective vehicle noise ratings. Long experience in the use of this index has shown that it consistently yields an improved correlation upon dBA with subjective response. It therefore provides an excellent engineering tool for the definition, and monitoring of structural and acoustic contributions to interior noise. However, this index was developed for vehicle sounds where the engine is the dominant source, with certain CRP parameters being influenced by the firing frequency of the engine. Increasingly, the vehicle noise environment is primarily influenced by road and wind noise, containing a significantly different energy distribution in the frequency domain compared with engine noise. This has prompted the need to redefine CRP for such applications, to allow road and wind noise to be characterised more precisely within the index. This was achieved through the analysis, and subjective assessment of a range of vehicle sounds containing road and wind noise characteristics. Through understanding the relationship of the third octave frequency bands to each other and to the overall level, a redefined CRP can be generated with independent components. This paper describes the derivation of this tentative new index, capable of accounting for spectral balance, and high frequency noise levels of road and wind noise, in addition to overall level.