From Wikipedia, the free encyclopedia
|This article does not cite any references or sources. (December 2008)|
|Media type||Magnetic Tape|
|Read mechanism||Helical scan|
|Write mechanism||Helical scan|
The Digital8 format is a combination of the older Hi8 tape transport with the DV codec. Digital8 equipment uses the same videocassettes as analog recording Hi8 equipment, but differs in that the signal is not analog audio/analog video, but is encoded digitally (using the industry-standard DV codec.) Since Digital8 uses the DV codec, it has identical digital audio and digital video specifications.
To facilitate digital recording on existing Hi8 videocassettes the helical scan video head drum spins 2.5x faster. For both NTSC and PAL Digital8 equipment, a standard-length 120-minute NTSC/90-minute PAL Hi8 magnetic tape cassette will store 60 minutes of Digital8 video (Standard Play) or 90 minutes (Long Play). LP is model specific, such as the TRV-30, TRV-40, and others. Digital8 recordings can be made on standard-grade Video8 cassettes, but this practice is discouraged in the Sony user manuals. Hi8 metal-particle cassettes are the recommended type for Digital8 recording, and most tapes currently sold are marked for both Hi8 and Digital8 usage.
MiniDV/DVC vs. Digital8
Contrary to popular perception, the Digital8 format is not technically inferior to miniDV -- both are identical at the bitstream level. From a user standpoint, Digital8 is DV (or rather, equivalent to and compatible with consumer miniDV.) At an application level (for example, in a 1394/Firewire link), a Digital8 camcorder appears and behaves exactly like a Mini DV camcorder.
Digital8 and Mini DV use different, non-interchangeable cassette media, with Digital8 cassettes being the physically larger of the two. The two formats may also use different media formulations: Digital8 can use metal-particle or metal-evaporated media, while miniDV is based solely on metal-evaporated media. The maximum recording time for Digital8 and MiniDV is 135 minutes and 130 minutes, respectively, using D-90 and DVM-85 tapes. These extra-thin, extra-long tapes are rare and expensive.   
In addition, Digital8 uses tape at 29mm per second; more like the higher-end DVCAM (28mm/s) and DVCPRO (34mm/s). MiniDV uses tape at 19mm/s. According to Sony's press release of January 7, 1999, for the MiniDV format one frame is recorded onto 10 tracks, with the Digital8 format one frame's worth of information is recorded vertically onto 25 tracks. The use of this recording method enables digital images to be recorded on a Hi8 tape.
While analog Hi8 video enjoyed widespread use by amateur home video, current affairs TV programs, and some professional news organizations, Digital8 seems to remain strictly a consumer (amateur) product. This is likely a reflection of Sony's design and market objectives for Digital8 format: to serve as a lower cost upgrade path for current customers (from analog 8 mm), by leveraging existing manufacturing infrastructure of 8 mm video equipment, and offering a familiar media format but with digital capabilities. Furthermore, Digital8 was released some time after miniDV, giving the rival DV format a lead in the professional market. While little or no Digital8 equipment has been produced for the professional market, there are no technical barriers opposing its development. In fact, Digital8 cameras have been used on the professional side of the film/TV business; example, Hall of Mirrors, The Movie.
The future of the Digital 8 format is in question as Sony, the format's original backer, is the only company still producing Digital8 equipment, and currently Sony has no plans to develop new Digital 8 cameras. Hitachi marketed a few Digital8 camcorders for a while but no longer does so. As of 2005 and later, Digital8 product line caters purely to the entry-level consumer. This is most likely because the larger, bulkier Digital8 cassette is perceived as an inferior technology, even though the Digital8 and DV formats offer indistinguishable A/V performance. In fact, the larger 8mm format is more robust, laying down wider tracks. Most, though not all, Digital8 camcorders can play back analogue Video8 and Hi8 tapes. As well as camcorders, Sony also released Digital8 Video Walkman Portables, the GV-D200 and GV-D800.
Camera Model Variations
In the early years after Digital8's introduction, Sony sold a product line with coverage from entry level to high-end consumer ("prosumer.") Although Sony never marketed by entry level or prosumer, there is, in fact, such variation. The more consumer oriented line uses a 1/6" CCD and the more prosumer line uses a 1/4" one. Both have existed from the beginning, but the 1/4" CCD models were quietly dropped at some point in time. (NOTE: The following information is general. See the owner's manual for the most accurate information on a given model.)
Some models allow an LP recording mode, thus giving 90 minutes on a standard Hi8 tape. Examples are the 2003 TRV-150, 250, 350, and 351 models. Interestingly, the owner's manual is the same for all of these models AND the TRV-118, 318, and 418 Hi8 versions. Both general variants use a tiny 3mm CCD, although the pixel count varies between the Digital8 (460K) and the Hi8 (320K) models.
Although the 1/4" CCD models are fully capable of taking a still photo, that is a secondary function and they lack the Sony Memory Stick feature to off load the jpeg images. Most of the entry level and later models focused on features such as better quality still pictures (see below), off loading the same via Sony Memory Sticks, and more programming selections. The combining of still image and video capture is now common, however a good still image CCD has different qualities from a good video CCD. The cameras also lost features generally appealing to a prosumer level customer. The 1999 TRV-310, for instance, has the 1/4" CCD,a full 3.5" LCD screen, now only found on the very professional Sony miniDV models, an f1.4 lens, variable shutter speed settings, manual focus, and other professional controls. The lens on a typical 1/6" CCD is f1.8, about 60% as fast as an f1.4. The TRV-310, has a 1/4" CCD with a pixel count of 460K and "effective count" of 290K. The larger CCD with fewer pixels allows a smaller depth of field for intentional blurred backgrounds in some situations unattainable with the 1/6" CCD. It also has greater light sensitivity, 1 lux vs. 7 lux for the 1/6" CCD (without Night Shot), and less sensor noise in low light conditions.
Another example of these capabilities changing with pixel count may be seen in the TRV-150, 250, 350, and 351 Digital8 models and their TRV-118, 318, and 418 Hi8 cousins. Despite having the same size CCD and the same f1.6 lens, the lower pixel count Hi8 models permit a 1 lux low light rating as compared to the 4 lux of the Digital8 models. The Sony DCR-TRV730/828/830 (and the later DCR-TRV740/840), were the only Digital8 camcorders to be built with a 1/4.7" (4.5mm) with advanced HAD (Hole Accumulation Diode)CCD. HAD is useful on smaller, high megapixel count CCD's and CMOS's. The pixel count for the TRV-730 is 1,070,000 pixels (690,000 in camera mode.)
Digital8 equipment cannot record in analog Video8/Hi8 format, but some equipment offers playback compatibility with 8 mm analog recordings. Even so, there are limitations, audio playback is limited to the Video8/Hi8 analog FM soundtrack and there is no inherent timestamping to edit with. Most Digital8 camcorders with analog playback also can simultaneously digitize the analog footage, sending the converted signal through the camcorder's FireWire interface to a computer with video capturing HW and SW. Such a conversion will have similar Video8/Hi8 audio and video quality to the original, but being digitized can be edited and used as video files or converted to DVDs.