AUDIO SYSTEM AND IN-VEHICLE SYSTEM

A sound output by an i-th audio source device is adjusted by an i-th sound leakage reduction filter with a frequency transfer function set in the i-th sound leakage reduction filter and is output from an i-th speaker toward a user. The frequency transfer function relatively reduces the volume of the sound at a frequency where a first gain of a frequency transfer function from the speaker to one or multiple predetermined sound leakage reference positions outside the vehicle tends to be high relative to a second gain of a frequency transfer function from the speaker to the user, and relatively increases the volume of the sound at a frequency where the first gain tends to be low relative to the second gain.