Abstract: When the instruction for increasing the volume level is input by the user's operation and the signal representing the set value or more is output from a detector, a controller does not increase the volume levels of the first volume controller and the second volume controller. When the signal representing the set value or more is not output from the detector and the second volume level has a predetermined value, the controller increases the first volume level. When the signal representing the set value or more is not output from the detector and the second volume level is less than the predetermined value, the controller increases the second volume level.

Abstract: When a signal representing a first set value or more is received from a detecting section, a determination is made whether a boost value is a predetermined value or more. When the boost value is the predetermined value or more, a currently set boost value is reduced by a predetermined step, so that a new boost value is set. Further, when the boost value is less than the predetermined value, a currently set volume level is reduced by a predetermined step, and a new volume level is set. Therefore, in a case when the set boost value is gradually reduced and the boost value is finally less than the predetermined value, the audio signal is still the first set value or more, the volume level is further reduced by each predetermined step. Therefore, an audio signal can be securely prevented from being clipped.

Abstract: When the instruction for increasing the volume level is input by the user's operation and the signal representing the set value or more is output from a detector, a controller does not increase the volume levels of the first volume controller and the second volume controller. When the signal representing the set value or more is not output from the detector and the second volume level has a predetermined value, the controller increases the first volume level. When the signal representing the set value or more is not output from the detector and the second volume level is less than the predetermined value, the controller increases the second volume level.

Abstract: When a signal representing a first set value or more is received from a detecting section, a determination is made whether a boost value is a predetermined value or more. When the boost value is the predetermined value or more, a currently set boost value is reduced by a predetermined step, so that a new boost value is set. Further, when the boost value is less than the predetermined value, a currently set volume level is reduced by a predetermined step, and a new volume level is set. Therefore, in a case when the set boost value is gradually reduced and the boost value is finally less than the predetermined value, the audio signal is still the first set value or more, the volume level is further reduced by each predetermined step. Therefore, an audio signal can be securely prevented from being clipped.