Frequently Asked Questions About CD-R and CD-RW Discs

Please contact Media Sciences if your questions are not answered on these pages.

What are the most important requirements of CD-R discs used for mastering?

Early CD-R discs were refused by some mastering facilities because they created serious problems. The reason is that laser beam recorders, or LBRs, often abort when they encounter certain conditions that may not affect a CD-R system. This ruins the expensive glass master, adding cost and delay to the replication process. Some mastering houses subsequently developed diverse methods to overcome CD-R problems. Since various organizations often use different methods, they may not repair all CD-R problems. It is therefore important to deliver high quality one-offs if you expect on-time delivery of high quality replicas.

Various format problems can adversely affect the mastering process. All compact disc formats have certain universal requirements including lead-in, pre-gap, post-gap, and lead-out. Lead-out must have a minimum length of 6750 sectors, or 90 seconds at 1X. It must contain 13 MBytes of null data, together with a special pattern in the subcode P channel. Not all CD-R premastering systems follow these rules, and LBR aborts or customer problems can occur.

Post-gap is a universal requirement for all discs including digital audio, CD-ROM, and CD-R formats. This 2 second, 150 sector region must contain only null data, must have all ONEs in the subcode P channel, must follow the last information track, and must precede lead-out. Mastering problems can occur if post-gap is missing, is too short, or if it contains actual data. Some premastering systems generate these flaws without the knowledge of the user.

Link blocks are regions containing uncorrectable errors that will abort LBR mastering. They "splice" valid information areas that were written at different times. Link blocks are not allowed by CD-ROM Standards and are absent in disc-at-once recording. Orange Book allows other methods such as track-at-once, multi-session, and packet recording that all produce link blocks. Since CD-R recorders and many modern CD-ROM drives comply with Orange Book requirements, they are not affected by link blocks. LBRs are definitely affected. Always use disc- at-once recording.

CD-ROM and CD-R systems provide sector level CIRC error correction that can detect and correct E32 "uncorrectable" errors from the C1/C2 error correction circuitry in the drive. Therefore, severe E32 errors may never be noticed at the premastering facility. Correction of these errors during mastering can interrupt the smooth data flow demanded by the LBR. Since LBRs normally abort upon receipt of such errors, E22 and E32 errors must always be avoided. Even if buffering permits LBR error correction, misdetects or miscorrects at the sector level can and do occur, resulting in faithful replication of the resulting flaw in every replica.

Proper testing can confirm many important quality indicators along with the absence of E22 and E32 errors. High reflectivity, low BLER and jitter, good HF and push-pull, low asymmetry and radial noise, and zero BURST errors all predict that your one-off will be readable in other drives including the important one that feeds the laser beam recorder.

LBRs demand a pristine flow of data in order to accurately generate the glass master. While writing, they must precisely control many properties such as track pitch, linear velocity, and pit geometry. If you follow the rules, your one-offs will lead to high quality masters, and the resulting replicas will successfully interchange in all acceptable drives. Break the rules and both mastering problems and customer returns will result.

Your CD-R "gold masters" should always conform to all requirements of ISO 10149 and ISO 9660, including post-gap and lead-out. Use disc-at-once recording to avoid link blocks. Testing should confirm media and drive quality using all quality indicators, and especially the requirement of no E22 or E32 errors. Unexpected problems can occur if you merely rely on data verification in a CD-R writer. Only comprehensive and accurate testing can provide the necessary level of confidence. Mastering and replication will then proceed smoothly, and the resulting replicas will be readable in all drives.