A mixed-mode CD includes more than one type of track format, usually Red Book audio and Yellow Book Mode 1 (ECC) information. Mixed-mode consists of a ROM track followed by any number of Red Book audio tracks. Mixed-mode has two problems: first, the CD-ROM track can be accidentally read by some audio players, causing an ugly static sound and potential speaker damage. Second, retailers don’t know whether to market the discs as music or data. See pregap, CD Extra.