Another of the CD format specifications released by Philips/Sony. Blue Book is also known as the CD-Extra format (in the Mixed-Mode family). It provides for including data and audio in the same disc. There have been a number of mixed mode disc standards (CD-Plus, Enhanced CD, etc.). Many of these use audio track #1 to store the CD-ROM data, which on some older CD players results in very loud digital noise playback where track one should be. The Blue Book fixes the ‘track one’ problem and can be read by current CD-Audio and CD-ROM drives.