Patent attributes
A variable gain amplifier (203: VGA) for amplifying an amplitude of a signal extracted by a pickup (202), an A/D converter (204) for converting the amplified signal into digital, and an amplitude detecting circuit (206) for detecting amplitude information from the digital information, are provided. A gain control circuit (205) for calculating a control value for the VGA (203) is calculated from the detected amplitude information, and an envelope generating circuit (207) for executing an operation of absorbing transfer characteristics of the VGA (203) from the control value for the VGA (203) and the amplitude information, are provided to generate an envelope extracted by the pickup (202). When the characteristics of the VGA (203) vary, a degree of the variation is calculated from the amplitude information of the signal extracted by the pickup (202) and amplitude information obtained by fixing the control value for the VGA (203), and characteristic correction is executed.
