DCC used a 9-track Magneto-Resistive (MR) head for playback. The head was fixed to the mechanism of the player/recorder, unlike rotary heads that are used in helical scan systems such as DAT or VHS to increase head-to-tape speed.
Because of the reduced number of moving parts, DCC players were less sensitive to shock and vibration. And because of the dimensions that were so similar to analog cassettes, existing auto-reverse audio cassette recorder mechanisms could easily be adapted for use in DCC-recorders simply by mounting a DCC head instead of an analog stereo head. In fact, Philips did this during development.
Magneto-resistive heads don't use iron so they don't build up residual magnetism. They never need to be demagnetized, and if a cassette demagnetizer is used on MR heads, they are easily damaged or destroyed.
Various head assemblies were used, according to the Service Manuals:
Stationary DCC-recorders (i.e. recorders meant for use in home stereo systems) such as the DCC-900 used a head assembly that had 9 (MR) playback tracks and 9 (coil) recording tracks for DCC, and two (MR) tracks for playing analog cassettes. This type of head assembly was designed to be rotated by the mechanism when the recorder/player switched from side A to side B.
Playback-only portable players such as the DCC-130 and DCC-134 used head assemblies with 18 MR tracks, nine for each side of the cassette. When playing analog cassettes, two of the MR tracks were used. The head assembly was fixed to the mechanism and didn't need to rotate for side B.
Portable recorders such as the DCC-170 and DCC-175 used head assemblies with 18 MR tracks for DCC playback, 18 coil tracks for DCC recording, and 4 MR tracks for analog playback (a total of 40 tracks in one head assembly). This head assembly was fixed to the mechanism and didn't need to rotate for side B.
Tape specifications and PASC audio compression
The tape speed of DCC was the same as for analog cassettes: 1 7⁄8 inches (4.8 cm) per second, and DCC cassettes used tape that was the same width as analog cassettes: 1/8 of an inch (3.175 mm). The tape that was used in production cassettes was chromium dioxide- or cobalt-doped ferric-oxide, 3-4 µm thick in a total tape thickness of 12 µm,[6] identical to the tape that was widely in use for video tapes.
Nine tracks were used to read/write half the width of the tape; the other half of the width was used for the B-side. Eight of these tracks contained audio data, the ninth track was 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 was 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 kHz, 44.1 kHz or 48 kHz, or they could record from analog sources at 44.1 kHz.
Because of the low tape speed, the achievable bit rate was limited. To compensate, DCC used an audio compression codec based upon MPEG-1 Audio Layer I (MP1) and termed PASC (Precision Adaptive Sub-band Coding). MPEG and PASC use digital filters to convert the audio into 32 frequency sub-bands, and then use adaptive allocation and scaling to decide how many bits should be assigned to represent each frequency band. When decoding, the sub-band bit stream is used to synthesize an uncompressed bit stream again.
PASC lowers the typical bitrate of a CD recording of approximately 1.4 megabits per second to 384 kilobits per second, a compression ratio of around 4:1. 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, time code) and adding Reed-Solomon error correction bits to the 384 kbit/s data stream, followed by 8b/10b encoding,[7] the resulting bit rate is 768 kbit/s, which is recorded onto the eight data tracks at 96 kbit/s per track in a checkered pattern.[8] According to the Philips webpage,[6] it was possible for a DCC recorder to recover all missing data off a tape even if one of the 8 audio tracks was completely unreadable, or if all tracks were unreadable for 1.45 mm (about 0.03 seconds).
Auxiliary track
On pre-recorded tapes, the information about album artist, album title and track titles and lengths was recorded in the auxiliary ninth track continuously for the length of the entire tape. This made it possible for players to recognize immediately what the tape position was and how to get to any of the other tracks (including which side of the tape to turn to), as soon as a tape was inserted and playback was started, regardless of whether the tape was rewound before inserting or not.
On user tapes, a track marker was recorded at the beginning of every track, so that it was possible to skip and repeat tracks automatically. The markers would be automatically recorded when a silence was detected during an analog recording, or when a track marker was received in the S/PDIF signal of a digital input source (this track marker would automatically be generated by CD players). It was possible to remove these markers (to "merge tracks"), or add extra markers (to "split tracks") without re-recording the audio. Furthermore, it was possible to add markers afterwards that would signal the end of the tape or the end of the tape side, so that during playback, the player would stop the mechanism or fast-forward to the end of the A-side or would switch from A-side to B-side immediately.
On later generations of recorders, it was possible to make a third tape type, referred to by service documentation as "super user tapes". The DCC-730 and DCC-951 made it possible to enter title information for each track, which was recorded on the auxiliary track after the start-of-track marker. Because the title information was only stored in one place, so unlike prerecorded tapes where users could see the names of all tracks on a tape, it wasn't possible to see tracks names of any other track than the one that was currently playing. Entering track information was a slow process (although easier with a remote control); only upper-case characters were supported and some commonly used symbols such as the apostrophe couldn't be entered.
The three tape types (prerecorded, user and super-user) are compatible with all recorders and it's impossible (and unnecessary) to recognize the difference between a user tape and a super-user tape without playing it. There were some interesting minor compatibility problems with text on super-user tapes; for example:
On stationary recorders that had simple fourteen-segment displays, all track information was converted to upper case. They were capable of displaying symbols that were impossible to enter with their own track info editors (such as the apostrophe), but they were unable to show lower case characters.
The Philips DCC-822 / DCC-824 car stereo with DCC player had a full dot-matrix text display which could display upper case and lower case titles from prerecorded tapes as well as super-user tapes
Later generation portable recorders DCC-134, DCC-170 and DCC-175 were capable of displaying text information from prerecorded tapes, but not from super-user tapes. The DCC-175 was capable of writing and reading the text information to/from a super-user tape via the PC, but didn't show the text information on the display.
Copy protection
All DCC-recorders used the SCMS copy protection system which uses two bits in the S/PDIF digital audio stream and on tape to differentiate between "protected" vs. "unprotected" audio, and between "original" vs. "copy":
Recording digitally from a source marked "protected" and "original" (produced by e.g. an audio CD or a prerecorded DCC) was allowed, but the recorder would change the "original" bit to the "copy" state on the tape to prevent further copying of the copy.
Recording digitally from a source marked "unprotected" was also allowed; the "original/copy" marker was ignored.
Recording digitally from a source marked "protected" and "copy" was not allowed: the record button would not work and any ongoing recordings would stop, and an error message would be shown on the display.
Analog recording was not restricted: tapes recorded from analog source were marked "unprotected". The only limitation to analog recording compared to DAT recorders was that the A/D converter was fixed to a sample frequency of 44.1 kHz. On the DCC-175 portable recorder it was possible to circumvent the SCMS protection by copying audio to the hard disk and then back to another tape, using the DCC-Studio program.
More recorders and players were introduced by Philips and other manufacturers in the following years, including some portable players and recorders as well as in-dash DCC/radio-receiver combinations for automotive use.
At the "HCC dagen" computer fair in Utrecht, The Netherlands, on November 24, 25 and 26, 1995, Philips presented the DCC-175 portable recorder that could be connected to an IBM-compatible PC using the "PC-link" cable. This was the first (and only) DCC recorder that could be connected to, and controlled by, a computer, and it was only ever available in the Netherlands.
Philips marketed the DCC format in Europe, the United States and Japan. According to the newspaper article that announced the demise of DCC, DCC was more popular than MiniDisc in Europe (especially in the Netherlands).
DCC was quietly discontinued in October 1996 after Philips admitted it had failed at achieving any significant market penetration with the format, and unofficially conceded victory to Sony. However, the MiniDisc format hadn't done very well either; the price of both systems had been too high for the younger market, and audiophiles rejected MD and DCC because in their opinion, the lossy compression deteriorated the audio quality too much.