# Optimization of Parametric Equalizer Filters in In-Vehicle Audio Systems with a Genetic Algorithm
## 3 Materials and Methods
### System Components and Modeling  
The in-vehicle audio system has a complex structure comprising multiple components. Key components include a signal generator, an audio analyzer, BNC connectors, a speaker, and a vehicle multimedia system. The transmission of signals starts with the input sound from the signal generator, traveling through BNC connectors to the audio analyzer, and then to the speaker. At the end of the signal process, the sound waves produced by the speaker are delivered to users via the in-vehicle multimedia system. These components are critical not only for the in-vehicle audio quality but also for directly influencing the auditory experience of drivers and passengers. The final output obtained in the vehicle audio system is the result of multiplying the frequency responses of the system components with each other. Therefore, the frequency response of each component is among the critical factors directly impacting system performance. The system diagram is shown in Figure 2. Subsequent sections will address the modeling of each component in terms of frequency response and examine the interactions between these responses. (A) Input Sound  
White noise is frequently preferred in the calibration processes of sound systems because it has equal sound intensity in a wide frequency range, such as 20 Hz-20 kHz. This feature allows for objective testing of the system's frequency response throughout the entire frequency band; thus, it enables a comprehensive analysis of system performance. Particularly in acoustic arrangements of sound systems and rooms, this broad-spectrum  
Figure 1: Normal equal-loudness-level contours for pure tones. sound source is utilized to assess system performance and the necessary adjustments are implemented. Consequently, the responses of sound systems at various frequencies can be objectively measured and optimized. A similar usage is found in in-vehicle sound systems. Thanks to its balanced and comprehensive frequency spectrum, white noise provides an ideal test signal for accurately detecting the frequency response of sound systems across a wide frequency range. A significant advantage is that during in-vehicle acoustic adjustments using white-noise signals, it is possible to interactively examine and adjust the effects of applied filters across all frequencies [6]. Acoustic analyzers use frequency weighting curves to simulate the human ear's sensitivity to different frequencies. The A, B, and C weighting scales, displayed in Figure 3, represent various frequency response filters employed in sound measurements. The process of weighting adjusts the measured decibel (dB) values of sounds at specific frequencies to match the sensitivity levels perceived by the human ear at those frequencies. Given the human ear's lower sensitivity to low frequencies and higher sensitivity to high frequencies, these weighting curves are essential for accurately reflecting perceived sound intensity. These curves aim to align the measured sound levels more closely with the natural response of the human ear and enhance the effective assessment of sound's true impact. Therefore, weighting filters are applied to the white-noise signal used as the input sound. Figure 3: Frequency weighted filters for A-, B-, and C-weightings [13]. Figure 2: In-vehicle audio system measurement diagram. A-weighting primarily represents the sensitivity of the human ear to ambient noise measurements at low sound levels. This scale is more sensitive between the frequencies of 500 Hz to 10 kHz, while it reduces sounds at lower and higher frequencies, making it ideal for everyday environmental sound measurements. B-weighting is designed for medium to high sound levels (80 to 90 phon) and emphasizes sounds across the frequency range slightly more, making it useful in environments such as cinema and music production. C-weighting is used at high sound levels and provides a flatter response across a wide frequency range. Thereby, low- and high-frequency sounds are measured at nearly their original levels.