Sound quality evaluation of non-stationary noise and its application to vehicle booming noise

Abstract

The target of noise control is now directed to the optimization of the product sound quality (PSQ) as well as the minimization of its sound pressure level (SPL). Most of the SQ evaluation has been based on the assumption that the sound is in a steady state or has a short duration. However, there are many cases with non-stationary characteristics that have relatively long duration. When the existing method is applied to such non-stationary sounds with long duration, there occur serious problems related to the time and cost for evaluation as well as the reliability and repeatability of the subjective response. The purpose of this study is to suggest a systematized method for the sound quality (SQ) evaluation of non-stationary noise without having abrupt change with time and having a duration longer than 3 seconds. In order to check the effectiveness of the suggested SQ evaluation method, the technique was applied to a demonstration example of the booming noise in the passenger car interior. In this study, the method for SQ evaluation of non-stationary sound with long duration is suggested in four parts. The first part is devoted to the method in obtaining the objective data using pitch concept and the representative SQ metrics such as loudness, sharpness, roughness, and fluctuation strength. For the application of the pitch to the SQ analysis of actual noise that can be frequently heard in our environment, the existing extraction algorithm by Terhardt was modified on the basis of empirical data related to the pitch perception. The second part describes the method to obtain the subjective data by performing four different types of listening tests. The purposes for these four different types of subjective tests are as follows: establishment of a guideline how to divide a long-term sound sample into several short-term sound samples, selection of the main variable influencing the SQ, estimation of the change of degree of the SQ with the main variable, extraction of a...