Engine sound enhancement and customization based on granular synthesis

Everyday car makers face important challenges in the automotive design and development. One of these is represented by the absence of acoustic feedback from the electric vehicles, leading to reduced safety for road users and worse driving experience, as engine sound is essential for taking decisions when traveling without the need for looking at the rev and speed indicators. Another core topic in the automotive field is the growing request for customization of the motor sound, aiming at making it more powerful and attractive for car users. This thesis work, developed in collaboration with the Electronics division of Marelli Europe S.p.A. located in Venaria Reale (TO), proposes a solution to emphasize the motor sound but also to create it in the case of noise-free vehicles, using a single recording of a thermal engine that identifies the vehicle acoustic fingerprint. After an overview on acoustics, the state of the art about systems which address car sound generation and enhancement is presented. Later, a model stating the relationship between perceived engine sound, car status parameters and noise sources is built up. Then, the practical activities performed to acquire a sound recording of an internal combustion engine along with the corresponding vehicle state variables (mainly engine speed, vehicle speed, engaged gear and acceleration) from the CAN bus are exposed. The designed procedure involves first the analysis of the audio recording and the extraction of its harmonic content from the stochastic noise sources that surround it. The resulting signal represents the input for the developed algorithm, granular synthesis based, which addresses the generation of a new sound depending on the operating conditions of the engine, identified by new vehicle state variables profiles, acquired in real-time from the on-board network. Sound customization is achieved by modulating independently the power content of each harmonic contribution of the audio signal, producing original sound textures. The presented solution provides quite pleasant and realistic engine sounds that can be played in the cabin and outside the vehicle.