COMMAND FILTERED-X LMS ALGORITHM AND ITS APPLICATION TO CAR INTERIOR NOISE FOR SOUND QUALITY CONTROL

In recent years, an increasing number of cars are being manufactured incorporating the active noise control (ANC) technology. This technology is being used not only for noise reduction but also for imparting the impression of an even engine running sound. Thus, engine sound control has shifted from noise reduction to sound design. To determine the desired engine sound, we investigate the relationship between each order component of the engine sound and the related auditory impression. The spectrum of each order component is not a constant level; it includes peaks and dips. In an auditory experiment, five stimuli obtained by signal processing, such as spectrum interpolation and elimination of a specific order component, were presented to 20 healthy volunteers and the scale values of preference were obtained using the semantic differential method. It was determined that the elimination of the second-order component improved the sporty feeling. Therefore, the engine sound impression can be changed by adjusting the spectrum power level, using ANC. To change the engine noise to the desired sound, we apply the command filtered-x LMS algorithm to an actual car. The harmonic structure of the car interior noise can be observed more clearly when controlled by this algorithm.