## 3 Discussion  
Based on the experiments in this study, an attempt was made to provide insight into the relationship between the signal and psychoacoustical parameters of passenger car sounds and the perceived annoyance ratings. The analyses, which were conducted in this study, show that L\({}_{\text{max}}\) gives better results than the corresponding average sound pressure level to characterize the perceived annoyance of passenger car pass-by noises. Although L\({}_{\text{max}}\) seems to be helpful in describing the perceived annoyance, both the average and maximum sound pressure levels can describe the perception only to a limited extent. Psychoacoustical properties, which are based on perceptual models, are helpful for considering the various perceptual characteristics of car pass-by sounds. Therefore, an annoyance index, which is based on loudness, tonality, roughness, and fluctuation strength, is developed in this study. The correlation between the developed index and annoyance ratings is very high. The results show that the psychoacoustically motivated annoyance index can be very helpful for estimating the perceived annoyance and accordingly noise-annoyance-based health problems. This result is in line with various studies that evaluated the auditory annoyance of pass-by noises, household appliances, and information technology devices [12; 13; 21; 24; 27; 43]. The analysis of the annoyance rating results and the panel discussion show that the perceived loudness of car pass-by sounds plays an important role in the perceived annoyance. The psychoacoustical property of loudness takes into account not only the frequency sensitivity of the human ear but also the spectral and temporal masking properties of the auditory system using a perceptually motivated ratio scale. Discrete tonal components, narrowband noise, and steep discontinuities in the noise spectra attract our attention more strongly than broadband noise alone [34]. STFT is helpful and was used in this study to identify the tonal components and their levels/frequencies in the pass-by sounds. A spectral analysis of car pass-by sounds using STFT shows that some of the sounds have strong tonal components. This is particularly true for electric cars, because in most cases electric motor or gear mechanisms produce strong tonal components. Additionally, the AVAS sounds mostly have a strong tonal character. In addition to loudness, the tonality should be taken into account for the estimation of the perceived annoyance. This finding is in agreement with our previous investigations, which underlined the importance of tonality not only for the perception of annoyance but also for the detection of car sounds [16; 17]. STFT analysis shows that car pass-by sounds have modulated components in some cases. This is true not only for ICE cars, where modulated components arise because of engine orders or diesel knocking, but also for electric cars, where tonal components occur within a critical band of human hearing. Such temporal variations, such as roughness, are strongly noticeable. Therefore, the psychoacoustical property of roughness is included in the annoyance index. The fluctuation strength is useful for considering the slow temporal variations of car pass-by sounds. To consider the nonstationary character of car pass-by sounds, which was discussed in Section 1, the 5 th percentile of the loudness and tonality values were taken into account. This kind of approach has also been applied in other psychoacoustical studies [14; 34]. The experts and participants have the opinion that the high frequency content of the pass-by sounds (dull/shrill) is important for the perceived annoyance. However, the sharpness values of the sounds were not meaningful for this aim. The analyses showed that the TETC is much more suitable for the characterization of the pass-by noise annoyance. This result was in line with the findings of [27]. However, a possible contribution of the TETC to the proposed annoyance index was negligible.