A White Paper for in-car measurements version 1.0 was officially published in 2023 by the Automotive Audio section of the AES. It comprises basic characteristics of car audio systems. One of the intentions was to make audio systems as well as different cars comparable. This paper is divided into two parts: In the first part, measurements of several cars with different sizes, ages, and audio performance are presented based on version 1. The feasibility of the suggested procedure is evaluated, and improvements are suggested. The first version addresses frequency responses at different levels and at maximum sound pressure level, as well as defect symptoms such as rattling. In a second part, additional measurements are suggested that address compression and non-linear distortion. The suitability of different distortion measurements is discussed and practically demonstrated. Time variant effects, which are typical for DSP-based algorithms, such as limiters, protection systems, and adaptive control, are also investigated, and methods to characterize those are proposed. Stationary behavior is not ensured in such systems; thus, methods to cope with transient effects are required.
