5.6.1 Introduction
5.6.1.1 Since their introduction in 1982 replicated optical disc media have become the dominant technology for distribution of published audio recordings. Recordable optical disc formats, first made available in the late 1980s1, play an increasingly significant role in distribution and storage of unpublished audio. Initially marketed as permanent, it has become clear that the usable life of the optical disc is finite and that steps will need to be taken to copy and preserve their data content. This is especially the case with recordable disc media, which are not only less reliable than their manufactured counterparts but are also more likely to contain unique material. Unless recorded and managed under specified conditions (see Section 6.6 Optical Discs: CD/DVD Recordables), recordable disc media constitute an unreasonable risk to collection material. This section of the Guidelines concerns itself with the accurate and efficient copying of CD and DVD optical disc media to more permanent storage systems. CD is the abbreviation for Compact Disc, DVD initially stood for Digital Video Disc, then Digital Versatile Disc but is now used without referring to a specific set of words.
5.6.1.2 The Audio CD family may include, in CD-DA format; CD manufactured, CD-R, CD-RW, and in this form are all characterised by 16 bit digital resolution, 44.1 kHz sampling frequency and 780nm wavelength read laser. DVD Audio includes SACD and DVD-A. Data formats such as .wav files and BWF files may be recorded as files on CD- ROM and DVD-ROM. DVD media are characterised by blue laser around 350 to 450nm for glass mastering and 635-650 nm playback, DVD+R (650 nm), DVD-R (both for authoring (635 nm laser)). Blu-Ray Discs (BD) are a high definition video and data format on the same diameter 12 cm disc as DVD and CD. Using a 405 nm blue laser BD is able to store 25 GB of data per layer.
5.6.1.3 Recordability, rewritability, erasability and accessibility:
5.6.1.3.1 CD and DVD (CD-, DVD-A, CD-ROM and DVD-ROM) discs are pre-recorded (pressed and moulded) read-only discs. They are neither recordable nor erasable.
5.6.1.3.2 CD-R, DVD-R and DVD+R discs are dye-based recordable (write once) discs, but not erasable.
5.6.1.3.3 CD-RW, DVD-RW and DVD+RW discs are phase-changed based repeatedly rewritable discs permitting erasure of earlier and recording new data in the same location on the disc.
5.6.1.3.4 DVD-RAM discs are phase-changed rewritable discs formatted for random access, much like a computer hard disc.
5.6.1.4 The table below (table 1 section 5.6) provides a listing of commercially available CD and DVD disc types.
| Disc | Type |
Storage capacity |
Laser wavelength write mode |
Laser wavelength read mode |
Typical use |
|---|---|---|---|---|---|
| CD-ROM, CD-A, CD-V | read only | 650 MB | 780 nm | 780 nm | Commercially available |
| CD-R (SS) | write once | 650 MB | 780 nm | 780 nm | Music recording, computer data, files, applications |
| CD-R (SS) | write once | 700 MB | 780 nm | 780 nm | |
| CD-RW (SS) | Rewritable | 650 MB | 780 nm | 780 nm | Computer data recording, files, applications |
| CD-RW (SS) | Rewritable | 700 MB | 780 nm | 780 nm | |
|
DVD-ROM, DVD-A, DVD-V: SS/SL SS/DL DS/SL DS/DL |
read only |
4.7 GB 8.54 GB 9.4 GB 17.08GB |
650 nm | 650 nm |
Movies, interactive games, programmes, applications |
| DVD-R(G) | write once | 4.7 GB | 650 nm | 650 nm |
General use: One time video recording and data archiving |
|
DVD-R(A) SL DL |
write once |
3.95 or 4.7 GB 8.5GB |
635 nm | 650 nm |
Authoring/professional use Video recording and editing |
|
DVD+R SL DL |
write once |
4.7 GB 8.5 GB |
650 nm | 650 nm |
General use: One time video recording and data archiving |
| DVD-RW | Rewritable | 4.7 GB | 650 nm | 650 nm | General use: Video recording and PC backup |
| DVD+RW | Rewritable | 4.7 GB | 650 nm | 650 nm | General use: Video recording and editing, data storage. PC backup |
|
DVD-RAM SS DS |
rewritable |
2.6 or 4.7 GB 5.2 or 9.4 GB |
650 nm | 650 nm | Computer data: Storage repository for updateable computer data, back-ups |
|
HD-DVD –R SL DL |
write once |
15 GB 30 GB |
405 nm | 405 nm | data and high-definition video |
|
HD-DVD –R W SL DL |
rewritable |
15 GB 30 GB |
405 nm | 405 nm | data and high-definition video |
|
BD-R SL DL |
write once |
25 GB 50 GB |
405 nm | 405 nm | data and high-definition video |
|
BD-RE SL DL |
rewritable |
25 GB 50 GB |
405 nm | 405 nm | data and high-definition video |
Table 1 Section 5.6 Commercially available CD/DVD disc types
SS= Single-sided, SL=Single layer, DL=double-sided, DL=dual layer
5.6.1.5 Under optimum conditions digital discs can produce an unaltered copy of the recorded signal, however, in the case of audio specific recordings, any un-corrected errors in the replay process will be permanently recorded in the new copy, or sometimes unnecessary interpolations will be incorporated into the archived data, neither of which is desirable. Optimisation of the transfer process will ensure that the data transferred is most closely equivalent to the information on the original carrier. As a general principle, the originals should always be kept for possible future re-consultation, however, for two simple, practical reasons, any transfer should attempt to extract the optimal signal from the best source copy. Firstly, the original carrier may deteriorate, and future replay may not achieve the same quality, or may in fact become impossible, and secondly, signal extraction is such a time consuming effort that financial considerations call for an optimisation at the first attempt
1. The first working CD-R system,Yamaha’s PDS (Programmable Disc System), was launched in 1988
