## 1 Introduction  
### Research Status of Sound Simulation Systems  
#### 1.1.1 Sound Design and Simulation Technology  
Many scholars have conducted relevant technical research on engine sound simulation systems. Initially, in 2001, [PERSON] and [PERSON] et al. proposed voiceless and voiced sounds, which are similar to speech processing techniques. In this concept, the engine sound signal is decomposed into a deterministic component and random component; the deterministic component is extracted using a synchronous discrete Fourier transform method, and the stochastic component is modeled using a new multipulse excited time-series modeling technique, which will determine the components and random component in order to synthesize the engine sound signal [1, 2, 3]. [PERSON] et al. connected the sound samples sequentially and used this method to simulate and synthesize the sound of the engine so that it could vary with speed and load during simulation [4]. [PERSON] et al. amplified or compressed the engine sound at different speeds by applying phase encoder technology to adjust the frequency of the sound signal, thereby simulating the engine sound of different states, but the relative amplitude of the sound harmonics is fixed. On this basis, [PERSON] measured the sound of the engine under different operating conditions and transposed and weighted it, correlating the relative amplitude of each harmonic of the sound with the engine speed [5, 6]. [PERSON], a Japanese researcher, designed the engine sound using signal processing methods, using the active sound technology in the car of an electric vehicle to simulate the engine sound [7]. In 2012, [PERSON] proposed a method to simulate the diesel engine idling sound by using Garber transform and time-frequency analysis for particle synthesis of diesel engine idling sound; however, this method is only applicable to diesel engine idling conditions and is not applicable in other operating conditions [8]. Based on the digital audio control algorithm, French technical researcher [PERSON] al. elaborated on the selection, comparison, and implementation of fitting parameters in active sound synthesis technology [9]. [PERSON] et al. proposed a method to simulate the sound at any engine speed by framing the sound samples into small fragments of milliseconds based on the principle of time-domain fundamental sound synchronization superposition technique in the field of speech synthesis, and by adaptively calculating and playing the sound fragments according to the change of engine excitation frequency [10]. Korean scholar [PERSON] studied sound design and subjective perception evaluation and concluded that when an electric vehicle accelerates, the sharp sensation of sound in the car decreases as the sound order in the low-frequency range increases [11]. [PERSON] et al. studied the changes in the influence of spatial sound field distribution caused by speaker placements on the characteristic parameters of simulated sound; [PERSON] proposed that the audio system composed of in-car speakers can be used for the active management of sound, and the order components of the sound of the car engine can be modified appropriately to achieve the purpose of sound modification. Subsequently, [PERSON] et al. used the car audio system to realize the sound simulation in the car and the warning sound prompt for pedestrians outside the car, and developed the acceleration sound with different auditory feelings according to the sound quality characteristics [12; 13; 14]. Regarding sound simulation system technology research, it has started a little late and mainly depends on research done in colleges and universities. The installation of a sound simulator was proposed by [PERSON] and others to solve the problem of electric vehicles that were too quiet. She also studied how to use voice processing software and related hardware systems in pure electric vehicle sound simulations [15].