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Vehicle Engine Sound Synthesis System

#项目#声音合成26
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This post is translated from Chinese into English through AI.View Original
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The document discusses a vehicle engine sound synthesis system that aims to create realistic engine sounds through physical modeling rather than traditional recording methods. It outlines the system's workflow, which involves determining vehicle parameters and simulating engine states based on user inputs like ignition and throttle position. The core algorithm focuses on how various physical parameters (such as RPM, air intake, fuel injection, ignition timing, exhaust pressure, cylinder pressure, temperature, engine load, and valve timing) affect sound characteristics. The synthesis process includes smoothing input signals, filtering, mixing, and adjusting levels before rendering the final sound output. The author notes that while the document provides a basic overview of the system, further development is needed for practical application in game engines, with ongoing efforts to make it more lightweight for integration into Unreal Engine.

Vehicle Engine Sound Synthesis System#

Product Demonstration#

Below is an audio clip of the Kohler-ch750 engine starting, idling, and adjusting the throttle.

engine_audio_20250401_101543.wav
engine_audio_20250401_101543.wav

Introduction#

In the field of game sound effects, the sound of vehicle engines has always been an important part.

Currently, mainstream methods often combine live recordings with real-time control through audio middleware to achieve a realistic engine sound. More advanced techniques can use particle synthesizers for better effects or control, such as the commonly used REV plugin on the Wwise platform, but fundamentally, this still requires sampling the sounds of various engine components.

This method clearly has various limitations.

This system will perform physical modeling based on the working principles of the engine. By simulating the modeling of the internal combustion engine's operation process to synthesize the final sound, it can achieve low latency, high-quality engine sound effects and provide real-time feedback.

Project Structure#

PS: Here we borrow the system structure diagram organized by @鲁旻荟 💕

image

The overall process of the system operation is:

First, determine the vehicle parameters, including: engine model, maximum RPM, number of cylinders, etc.

Next, through user real-time operations such as starting ignition, shutting off, changing gears, and throttle position, influence important parameters like engine RPM and throttle opening to change the state of the engine simulator.

In the loop, the simulator will begin physical simulation calculations of the engine under vehicle operating conditions based on the real-time status of the engine. By simulating the fluid dynamics of the intake and exhaust systems, as well as calculating exhaust flow, engine RPM, attenuation coefficients, etc., it determines the characteristics and intensity of the sound.

Finally, the results are written into the synthesizer (Synthesizer class). The synthesizer will convert the simulated engine RPM and exhaust volume data into a simulated engine sound signal through calculations, then feedback to the Simulator class to generate real-time dynamic engine sound signals, which are played back through audio output devices.

Core Algorithm#

First, how physical parameters affect sound intensity and timbre:

(Overall, it is through a series of physical parameters that ultimately affect the flow of the exhaust system, thereby changing the fundamental frequency of the sound; at the same time, other engine module parameters change the timbre.)

  1. Engine RPM:
    The higher the RPM, the higher the exhaust frequency, leading to an increase in the frequency of exhaust pulses, which in turn raises the sound frequency.
  2. Intake Flow:
    An increase in intake volume usually leads to more complete and intense combustion, resulting in greater exhaust flow and louder sound.
  3. Fuel Injection Amount:
    More fuel injection leads to more intense combustion, generating higher pressure and exhaust flow, making the sound louder.
  4. Ignition Timing:
    Advancing or delaying the ignition timing changes the characteristics of the combustion process, affecting combustion efficiency and pressure fluctuations, thereby influencing exhaust flow and sound characteristics.
  5. Exhaust System Pressure:
    Pressure changes in the exhaust system directly affect the dynamic characteristics of exhaust flow and the propagation of sound.
  6. Cylinder Pressure:
    The frequency and amplitude of pressure fluctuations within the cylinder affect the pulsing characteristics of exhaust flow, thereby influencing sound frequency and intensity.
  7. Heat and Temperature:
    Temperature changes affect the expansion rate of gases and the stability of exhaust flow, thus influencing sound characteristics.
  8. Engine Load:
    Load changes affect the intensity and frequency of the combustion process, thereby altering exhaust flow and sound.
  9. Timing and Duration of Intake and Exhaust Valve Openings:
    The timing of intake and exhaust valves affects the efficiency of gas exchange within the cylinder, changing the pulsing characteristics of exhaust flow and sound.
  10. Vibration and Resonance:
    The vibration characteristics of the engine and its components influence the modulation of exhaust flow and the spectral characteristics of sound through the vibration patterns of the exhaust system.

Next, how the sound synthesis system synthesizes sound signals through these parameters:

  1. First, the exhaust flow signal is input into the synthesizer, and its input values are interpolated and smoothed.
    image 1

  2. Signal DC filtering.
    image 2

  3. Signal differentiation.
    image 3

  4. Air noise low-pass filtering.
    image 4

  5. Signal mixing.
    image 5

  6. Convolution filtering.
    image 6

  7. Level adjustment.
    image 7

  8. Signal quantization.
    image 8

  9. Finally, render the signal to the audio output device.

Summary and Outlook#

Currently, this article only provides a rough introduction to some core parts of the entire system; in reality, there are many specific details that have not been elaborated. Due to its complex calculations and physical modeling, this system is not yet suitable for direct application in game engines. As of the completion of this article, the author has been working on further lightweighting efforts and is committed to achieving its integration into the UE engine.

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