## 2 Materials and Methods
### Identifying Torque-Dependent Tire Noise Components  
To evaluate the components of the masking tire noise in the vehicle interior that are torque-dependent, the following assumptions, with regard to future application to road measurements, have been made:  
* Aerodynamic noises are not torque-dependent. * The torque-dependent tire noise spectrum on the roller dynamometer is comparable to the torque-dependent tire noise spectrum on the road. To identify the relevant tire noise spectrum, roller dynamometer measurements offer the significant advantage that these measurements do not contain any wind noise and the tire noise can be evaluated separately. However, the masking noise generated during roller dynamometer measurements shows substantial differences compared to road driving conditions. In particular, the absence of aerodynamic noise and the pronounced increase in tire noise distinguish these measurements from those on the road [13]. In order to evaluate the tire noise separated from the powertrain noise, the tonal components of the powertrain were eliminated using a coherence filtering method of the signal processing program RAWLAB RL[t] v1.31 [34]. The program provides a specialized filter that is designed to separate signals that are coherent with a reference signal, such as torsional speed, from incoherent contributions. In this way, powertrain noises can be separated from the masking noise. To identify the relevant tire noise components on the roller dynamometer, comparisons were made between measurements using summer tires and treadless slick tires, as already presented in [13]. The use of slick tires significantly reduces tire noise. The Campbell diagrams in Figure 2 show roller dynamometer measurements with summer tires (Figure 2a) and slick tires (Figure 2b). The distinct characteristics can clearly be seen. Figure 2a illustrates the primary tread orders of the tires, which constitute the first block harmonic. Using slick tires, this order band becomes noticeably less prominent and can be directly associated with the tire noise (Figure 2a) [13]. Additionally, a broad frequency band in the higher frequency range can be seen in Figure 2a, which is also less pronounced with slick tires. As already shown in [13], the sound pressure level of the block harmonic and the masking thresholds for orders that cover the same frequency range as the block harmonic are strongly torque-dependent as the sound pressure level of the block harmonic is highly sensitive to torque. Figure 3 shows the masking threshold corresponding to the engine order in the center of the block harmonic across a torque range of 0 Nm to 500 Nm. Variations  
Figure 2: Campbell diagrams displaying roller dynamometer results for summer tires (**a**) and treadless slick tires (**b**) [13]. in the masking threshold of up to 7 dB can be observed, which can be attributed to the increased snap-out effects of the tread blocks under tire torque [31]. Similar observations can be made for the second block harmonic. Besides the block harmonic, an increase in high-frequent noise components can also be seen in Figure 2. This is caused by the increased noise due to sliding of the contact patch and the more violent snap-out of the tread blocks under torque [32]. To illustrate the torque dependency of these high-frequent noise components, the signals were filtered using a bandpass filter that extracts the relevant frequency range. Figure 4 shows the sound pressure level of the high-frequency noise components of the luxury vehicle at 200 Nm and 570 Nm. Over the entire speed range, the sound pressure level of the high-frequency components is significantly increased at 570 Nm (green line) compared to 200 Nm (red line). In summary, the following two tire contributions are identified:  
* First and second block harmonic;
* High-frequency noise components.