A technique to enhance audio quality of a quantized audio signal when a perceptual audio coder is operating at low bit rates. The filter is formed as a strip shaped, long and thin plate that is made from a transparent material that has a refractive index that is larger at least than that of air. The surface is arranged to face the passenger and is positionable so that a distance between the surface and the passenger is changeable. In addition, the method checks whether the short message has the first weight value or the second weight value, and backups the short message to the storage device if the short message has the first weight value, or deletes the short message from the message folder if the short message has the second weight value. This coating exhibits a high corrosion resistance, a relatively high hardness level and good adhesion to secondary coatings.