The Digital Audio Stationary Head or DASH standard is a reel-to-reel, digital audio tape format introduced by Sony in early 1982 for high-quality multitrack studio recording and mastering, as an alternative to analog recording methods. DASH is capable of recording two channels of audio on a quarter-inch tape, and 24 or 48 tracks on 1⁄2-inch-wide (13mm) tape on open reels of up to 14 inches. The data is recorded on the tape linearly, with a stationary recording head, as opposed to the DAT format, where data is recorded helically with a rotating head, in the same manner as a VCR. The audio data is encoded as linear PCM and boasts strong cyclic redundancy check (CRC) error correction, allowing the tape to be physically edited with a razor blade as analog tape would, e.g. by cutting and splicing, and played back with no loss of signal. In a two-track DASH recorder, the digital data is recorded onto the tape across nine data tracks: eight for the digital audio data and one for the CRC data; there is also provision for two linear analog cue tracks and one additional linear analog track dedicated to recording time code.
Digital audio recorders are fundamentally high bit-rate data recorders storing PCM encoded audio data. The main advantage of any digital recording medium is that of consistent, flat frequency response, high dynamic range audio reproduction compared to analog tape recorders, which is why some of the first uses of digital audio recording were for classical music. To further increase usable dynamic range, early DASH recorders included a specialized circuit called "Emphasis" which was intended to help overcome the noise of analog to digital and digital to analog converters of the time by boosting high frequencies on the front end. This circuit required complimentary de-emphasis on playback after the DAC for accurate reproduction. While emphasis was almost a necessity in earlier units, the circuit, of course, had a sound of its own and was used less and less as converter design improved.
There were three families of DASH recorders produced by Sony and Studer, with few differences among them:
48 track: PCM-3348, PCM-3348HR, and the Studer D820 and D827
TASCAM also produced a 24-track DASH recorder, the DA-800/24.
With the exception of the Sony PCM-3348HR and Studer D827, all of the DASH recorders have 16-bit resolution with a 44.1kHz or 48kHz sampling rate, although it is possible to use an outboard analog-to-digital converter of up to 20-bit resolution. The PCM-3348HR and D827 are capable of 24-bit 48kHz operation at 45 ips, and are the only machines that still find significant use today, often in only the highest-end studios for music and film production. All DASH recorders primarily use the SDIF-2 (Sony Digital Interface Format-2) as a digital interface, which is slightly different from the S/PDIF or AES3 that nearly all other digital audio recorders use, but is technically superior because SDIF-2's word clock is not multiplexed into the bitstream.
Because SDIF-2 is often only found on the expensive DASH recorders, it is also often only found on the highest-end mixing consoles, such as those made by Solid State Logic.
Tape
One significant advantage offered by DASH recorders over the analog recorders of the day was that 'proper' tape biasing was unimportant, as there is no means for the tape to 'color' the sound of the recorded data. This was a nice advantage, and routine maintenance amounted to not much more than keeping the tape guides clean. Due to this fact, the formulation of tape does not change the sound quality, unlike analog machines which must be set for specific formulae.
The 2-track DASH machines use 1/4" wide tape, while the 24 and 48 track versions use 1/2" wide tape. One interesting thing of note is that the 24-track machines only utilize half of the tape's width, and can be played on the 48-track machines with no modifications. Similarly, the 48-track tapes can be played on a 24-track machine, but only the first 24 tracks are capable of being reproduced.
DASH recorders (as well as any other type of digital recorder using magnetic tape) require the use of metal-particle formulation magnetic tape. Some examples of metal particle tape compatible with DASH machines are 3M Scotch 275, Ampex / Quantegy 467, EMTEC 931, and Sony's own tape formulation. These tape formulations are not directly compatible with any analog open-reel tape recorder.
The DASH format is not compatible with the only other popular open reel stationary head digital recording format, Mitsubishi's ProDigi, which was available as 2-, 16-, and 32-track variations.
Digital audio is a representation of sound recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is typically encoded as numerical samples in a continuous sequence. For example, in CD audio, samples are taken 44,100 times per second, each with 16-bit sample depth. Digital audio is also the name for the entire technology of sound recording and reproduction using audio signals that have been encoded in digital form. Following significant advances in digital audio technology during the 1970s and 1980s, it gradually replaced analog audio technology in many areas of audio engineering, record production and telecommunications in the 1990s and 2000s.
DV refers to a family of codecs and tape formats used for storing digital video, launched in 1995 by a consortium of video camera manufacturers led by Sony and Panasonic. In the late 1990s and early 2000s, DV was strongly associated with the transition from analog to digital desktop video production, and also with several enduring "prosumer" camera designs such as the Sony VX-1000. DV is sometimes referred to as MiniDV, which was the most popular tape format using a DV codec during this time.
Digital Audio Tape is a signal recording and playback medium developed by Sony and introduced in 1987. In appearance it is similar to a Compact Cassette, using 3.81 mm / 0.15" magnetic tape enclosed in a protective shell, but is roughly half the size at 73 mm × 54 mm × 10.5 mm. The recording is digital rather than analog. DAT can record at sampling rates equal to, as well as higher and lower than a CD at 16 bits quantization. If a comparable digital source is copied without returning to the analogue domain, then the DAT will produce an exact clone, unlike other digital media such as Digital Compact Cassette or non-Hi-MD MiniDisc, both of which use a lossy data-reduction system.
Sound can be recorded and stored and played using either digital or analog techniques. Both techniques introduce errors and distortions in the sound, and these methods can be systematically compared. Musicians and listeners have argued over the superiority of digital versus analog sound recordings. Arguments for analog systems include the absence of fundamental error mechanisms which are present in digital audio systems, including aliasing and associated anti-aliasing filter implementation, jitter and quantization noise. Advocates of digital point to the high levels of performance possible with digital audio, including excellent linearity in the audible band and low levels of noise and distortion.
S-VHS (スーパー・ヴィエイチエス), the common initialism for Super VHS, is an improved version of the VHS standard for consumer-level video recording. Victor Company of Japan introduced S-VHS in Japan in April 1987, with their JVC-branded HR-S7000 VCR, and in certain overseas markets soon afterward. By the end of 1987, the first S-VHS VCR models from other competitors included Hitachi VT-2700A, Mitsubishi HS-423UR, Panasonic PV-S4764, RCA VPT-695HF, and Toshiba SV-950. It has been standardized as IEC 60774-3 and IEC 60774-4.
Nagra is a brand of portable audio recorders produced from 1951 in Switzerland. Beginning in 1997 a range of high-end equipment aimed at the audiophile community was introduced, and Nagra expanded the company's product lines into new markets.
The Digital Compact Cassette (DCC) is a magnetic tape sound recording format introduced by Philips and Matsushita Electric in late 1992 and marketed as the successor to the standard analog Compact Cassette. It was also a direct competitor to Sony's MiniDisc (MD), but neither format toppled the then-ubiquitous analog cassette despite their technical superiority, and DCC was discontinued in October 1996.
Reel-to-reel audio tape recording, also called open-reel recording, is magnetic tape audio recording in which the recording tape is spooled between reels. To prepare for use, the supply reel containing the tape is placed on a spindle or hub. The end of the tape is manually pulled from the reel, threaded through mechanical guides and over a tape head assembly, and attached by friction to the hub of the second, initially empty takeup reel. Reel-to-reel systems use tape that is 1⁄4, 1⁄2, 1, or 2 inches wide, which normally moves at 3+3⁄4, 7+1⁄2, 15 or 30 inches per second. Domestic consumer machines almost always used 1⁄4 inch (6.35 mm) or narrower tape and many offered slower speeds such as 1+7⁄8 inches per second (4.762 cm/s). All standard tape speeds are derived as a binary submultiple of 30 inches per second.
Direct Stream Digital (DSD) is a trademark used by Sony and Philips for their system for digitally encoding audio signals for the Super Audio CD (SACD).
Betacam is a family of half-inch professional videocassette products developed by Sony in 1982. In colloquial use, "Betacam" singly is often used to refer to a Betacam camcorder, a Betacam tape, a Betacam video recorder or the format itself.
A video tape recorder (VTR) is a tape recorder designed to record and playback video and audio material from magnetic tape. The early VTRs were open-reel devices that record on individual reels of 2-inch-wide (5.08 cm) tape. They were used in television studios, serving as a replacement for motion picture film stock and making recording for television applications cheaper and quicker. Beginning in 1963, videotape machines made instant replay during televised sporting events possible. Improved formats, in which the tape was contained inside a videocassette, were introduced around 1969; the machines which play them are called videocassette recorders.
In digital recording, an audio or video signal is converted into a stream of discrete numbers representing the changes over time in air pressure for audio, or chroma and luminance values for video. This number stream is saved to a storage device. To play back a digital recording, the numbers are retrieved and converted back into their original analog audio or video forms so that they can be heard or seen.
The 8mm video format refers informally to three related videocassette formats. These are the original Video8 format and its improved successor Hi8, as well as a more recent digital recording format known as Digital8. Their user base consisted mainly of amateur camcorder users, although they also saw important use in the professional television production field.
D-2 is a professional digital videocassette format created by Ampex and introduced in 1988 at the NAB Show as a composite video alternative to the component video D-1 format. It garnered Ampex a technical Emmy in 1989. Like D-1, D-2 stores uncompressed digital video on a tape cassette; however, it stores a composite video signal, rather than component video as with D-1. While component video is superior for advanced editing, especially when chroma key effects are used, composite video was more compatible with most analog facilities existing at the time.
A PCM adaptor is a device that encodes digital audio as video for recording on a videocassette recorder. The adapter also has the ability to decode a video signal back to digital audio for playback. This digital audio system was used for mastering early compact discs.
Soundstream Inc. was the first United States audiophile digital audio recording company, providing commercial services for recording and computer-based editing.
The history of sound recording - which has progressed in waves, driven by the invention and commercial introduction of new technologies — can be roughly divided into four main periods:
D-9 or Digital-S as it was originally known, is a professional digital video videocassette format created by JVC in 1995.
Multitrack recording of sound is the process in which sound and other electro-acoustic signals are captured on a recording medium such as magnetic tape, which is divided into two or more audio tracks that run parallel with each other. Because they are carried on the same medium, the tracks stay in perfect synchronization, while allowing multiple sound sources to be recorded at different times.
Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
