Editing Digital Compact Cassette (section)

=== Tape specifications and PASC audio compression ===

DCC tape is the same {{convert|0.15|in|mm}} width as in analog compact cassettes, and operates at the same speed: {{convert|1+7/8|in|cm}} per second. The tape that was used in production cassettes was chromium dioxide- or cobalt-doped [[ferric oxide]], 3–4&nbsp;μm thick in a total tape thickness of 12&nbsp;μm,<ref name="Philips DCC page">[https://www.dcc-faq.org/philips/dcc.html Philips DCC page] preserved as part of the [https://www.dcc-faq.org DCC FAQ page]</ref> identical to the tape that was widely in use for video tapes.

Nine heads are used to read/write half the width of the tape; the other half of the width are used for the B-side. Eight of these tracks contain audio data, the ninth track is used for auxiliary information such as song titles and track markers, as well as markers to make the player switch from side A to side B (with or without winding towards the end of the tape first) and end-of-tape markers.

The (theoretical) maximum capacity of a DCC tape is 120 minutes, compared to 3 hours for DAT; however, no 120-minute tapes were ever produced. Also, because of the time needed for the mechanism to switch direction, there is always a short interruption in the audio between the two sides of the tape. DCC recorders could record from digital sources that used the [[S/PDIF]] standard, at sample rates of 32&nbsp;kHz, 44.1&nbsp;kHz or 48&nbsp;kHz, or they could record from analog sources at 44.1&nbsp;kHz.{{cn|date=May 2017}}

Because of the low tape speed, the achievable [[bit rate]] of DCC is limited. To compensate, DCC uses Precision Adaptive Sub-band Coding (PASC) for [[audio data compression]]. PASC was later integrated into the ISO/IEC 11172-3 standard as [[MPEG-1 Audio Layer I]] (MP1). Though MP1 allows various bit rates, PASC is fixed at 384&nbsp;[[kilobits]] per second. The bandwidth of a CD recording of approximately 1.4<!--44100*16*2=1411200--> [[megabits]] per second is reduced to 384 [[kilobits]] per second, a compression ratio of around 3.68:1. The difference in quality between PASC and the 5:1 compression used by early versions of [[ATRAC]] in the original MiniDisc is largely a subjective matter.

After adding system information (such as emphasis settings, SCMS information, and time code) as well as adding [[Reed-Solomon error correction]] bits to the 384 kbit/s data stream, followed by [[8b/10b encoding]],<ref>{{US patent|4,620,311}}Method of transmitting information, encoding device for use in the method, and decoding device for use in the method, June 1986.</ref> the resulting bit rate on the eight main data tracks tape ends up being twice the rate of the original PASC data: 768&nbsp;kbit/s, which is recorded onto the eight main data tracks at 96&nbsp;kbit/s per track in an interleaved pattern.<ref>[http://www.cieri.net/Documenti/Documenti%20audio/Digital%20Compact%20Cassette%20(DCC)%20-%20Matsushita%20and%20Philips%20Develop%20New%20Standard.pdf Digital Compact Cassette (DCC) - Matsushita and Philips Develop New Standard]. Retrieved 2017-01-16.</ref> According to the Philips webpage,<ref name="Philips DCC page"/> it is possible for a DCC player to recover all missing data from a tape, even if one of the 8 audio tracks is completely unreadable, or if all tracks are unreadable for 1.45&nbsp;mm (about 0.03 seconds).