The acoustical frequency response of an automobile audio system, measured at the listener position, is usually far from ideal. It is therefore desirable to equalize this response electronically in the audio system. Equalization can be implemented with common analog filter circuits, but these are susceptible to performance variations due to temperature and part tolerances. As a result, the design of an analog equalization circuit can be time consuming, requiring several design, build and test iterations to achieve the desired response. In addition, due to limits in analog circuit capabilities, the design may only yield an approximate response correction.
Frequency response modification, particularly for the purpose of equalization, is a popular application of digital signal processing (DSP). This paper describes a DSP-based vehicle equalization design system. It uses a DSP unit in the vehicle for performing the equalization, and a personal computer (PC) for controlling the unit. The PC is used by the automotive audio engineer to set the equalizer response of the DSP unit for a particular vehicle model. Once the response is set, the resulting equalization parameters are saved to disk. These parameters can then be used in any automotive audio system having DSP capabilities. This system produces exact, repeatable equalizer performance, and greatly reduces equalizer design time.