## 3 Design of Motion-Sensitive Sound Samples
### Sound Sample Order Analysis  
The collected sound was initially screened, and the sound signal playback function in LMS Test. Lab was used to initially eliminate the disturbed and unstable sound samples in the collection process, and a more ideal group of samples was selected for spectral analysis, as shown in Figure 6 for the sound time domain signal of the intercepted section of acceleration noise in the car under the third gear acceleration condition.  
The selected acceleration engine sound in third gear can well-reflect the process of acceleration sound change of the vehicle, and the analysis process of other gears is the same. Here, the acceleration sound analysis in third gear is taken as an example. Spectrum analysis and order tracking extraction were performed on the selected sound segments to observe the energy distribution of each order. Figure 7 shows the noise spectrum in the car under the acceleration conditions.  
It can be observed that in Figure 7, the noise energy in the car is mainly distributed in the low frequency range of 0-800 Hz, showing an energy distributi  
Figure 6: In-vehicle sound signal for acceleration conditions.  
Figure 7: Acceleration noise spectrum in the vehicle under acceleration conditions.  
and odd orders and supplemented by half-order noise, in which the energy of orders greater than or equal to 10 is very weak, so only the order composition and energy distribution of the first 8 orders are considered in the analysis. The 1 st and 2 nd order noise order harmonic slices are shown in Figure 8. These two order lines are the two orders with the weakest and strongest spectral energy in the section of noise, respectively, and the other order curves lie roughly within the interval of these two orders.  
The even-order noise of a four-stroke engine has a certain impact on the sense of acceleration power, and the odd-order or half-order energy will increase the sound roughness, which has a certain correlation with the subjective feeling of movement [51]. From Figure 7, it can be concluded that the order noise part of the engine sound is mainly composed of odd, even, and half-order noise, so the influence of the acceleration sound composed of these different order noises on the auditory perception of the sense of motion is mainly studied. Table 2 shows the designed order adjustment scheme with samples 1 to 6, indicating the decay and retention for odd, even, and half orders, respectively.  
Six groups of different order compositions are designed to produce the sound, filter out the sound within 1000 Hz by low-pass filter, use the adaptive trap filter to adjust the order composition to achieve the order on the harmonic attenuation, enhancement, and minimize the impact on the adjacent harmonics. The notch filter is defined by its center value, width, and attenuation factor, which are expressed as frequency in the time domain and as order in the frequency domain. After analysis and comparison, the harmonic order that the accelerated sound sample needs to be processed is set with a width of 0.15 and an attenuation factor of 40, which can track the corresponding order harmonic noise well. The notch filter order tracking principle is shown in Figure 9.  
\begin{table}
\begin{tabular}{c c} \hline
**Sample Number** & **Order Adjustment** \\ \hline YB 1 & \(-O_{1}-O_{3},-O_{5},-O_{7}\) \\ YB 2 & \(-O_{2}-O_{4},-O_{6},-O_{8}\) \\ YB 3 & \(O_{1},O_{3},O_{5},O_{7}\) \\ YB 4 & \(O_{2},O_{4},O_{6},O_{8}\) \\ YB 5 & \(O_{2,5},O_{3,5},O_{4,5},O_{5,5},O_{6,5},O_{7,5}\) \\ YB 6 & \(O_{1},O_{2},O_{3},O_{4},O_{5},O_{6},O_{7},O_{8}\) \\ \hline \end{tabular}
\end{table}
Table 2: Order regulation scheme.  
Figure 8: Order harmonic slicing curve.  
Six groups of sound samples with different order distributions were obtained. Figure 10 shows the spectrum of the sound samples after order adjustment.