Digital Audio Tape (August 2022)
From the 1950s through the 1970s, the primary medium for playing music was the vinyl record, mostly LPs, but also 45s. Record players, of course, offered no portability. That need was fulfilled by the transistor radio, though it lacked the ability to play on demand what one wanted to listen to. Compact Cassettes rose as an alternative to records, and small players like Sony’s Walkman (introduced in 1979) provided portability and music quality that improved over the following two decades. (Let’s not forget boomboxes!) Also, cassette devices have the capability to record, a feature fostering the popularity of mix tapes, among other uses.
Paralleling this analogue music device timeline, digital audio capabilities were being developed by several companies during the 1960s, 1970s, and early 1980s. Digital audio promised music without records’ surface noise or cassettes’ tape hiss, a much greater dynamic range, and a better low-frequency response than any of the popular media of the time (see The Vinyl vs. CD Debate, Part 2: Technical Factors). The first Compact Disc (CD) was released in 1982; Sony introduced the CD Walkman in 1984 (then known as Discman); and CDs began overtaking LPs as the dominant source of music sales. However, CD players, like record players, lacked the capability to record.
Audio technology companies, notably Sony and Philips, envisioned another digital format that would provide a recording function and come to supplant cassettes: Digital Audio Tape (DAT). After DAT recording standards were established in 1985, consumer product development ramped up, and DAT devices and tapes became available to the Japanese and European public in 1987. Introduction of home and personal digital audio recording devices in the U.S. was delayed because the recording industry, concerned about the ability to make perfect clones of audio tracks, feared rampant, unlicensed copying and sharing of music and was lobbying Congress for protections. Compromise legislation was eventually enacted (Audio Home Recording Act of 1992).
DAT devices offer another capability present in CDs but lacking in cassettes. They can display track numbers and enable the user to skip forward or backward directly to a different track rather than relying on the guesswork of fast-forwarding or rewinding a cassette.
DAT Technology
Analogue magnetic tape devices transport tape across stationary read and playback heads, which impart magnetization to the tape during recording or “read” the tape’s magnetization during playback, both occurring longitudinally along the length of the tape. Tape speeds across the heads vary from 15/32 inches per second (ips) for Microcassettes recording at half-normal speed (poor audio quality) to 30 ips on reel-to-reel tape decks (studio quality). Because digital audio requires significantly more data than analogue recordings, tape speed across the head would need to be feet per second, which would use up a lot of tape if DAT had used the analogue approach of writing data longitudinally.
The development of DAT went a different direction, taking advantage of the widely successful technology used in video recorders. To achieve the required speed of the tape across the head, DAT devices incorporate two heads mounted in a drum that spins at 2000 rpm. As with VCRs, the drum is mounted at an angle with respect to the tape, and the tape is wound partially around the drum—about 270 degrees in a VCR, about 90 degrees in a DAT recorder. From the drum’s perspective, the tape makes contact near one edge and spirals toward the other, giving rise to the term helical scan. What is written onto the tape, and later played back, is a series of adjacent diagonal stripes of digital information. With the rapidly spinning drum, the speed of the data in the diagonal stripes across the head is about 122 ips, a little over 10 feet per second. But because the diagonal stripes are so narrow (13.6 microns), the transport speed of DAT tape from spool to spool needs to be only ~0.32 ips, which uses a lot less tape.
Audio information written onto DAT tapes usually has a sampling rate of 44.1 KHz (44,100 samples per second) and a bit depth of 16 (i.e., a sample can take on any of two to the 16th, or 65,536, possible values). Those are the same parameters used for CDs. Other DAT combinations are 48.0 KHz/16-bit (a slight nod toward high resolution), 32.0 KHz/16-bit (at half speed to double the recording time), and 32.0 KHz/12-bit. Some devices are capable of 96.0 KHz/24-bit (high resolution), but devices capable of reading that resolution are less common. (See Digital Audio Resolution for a discussion of these parameters.)
DAT recordings contain two types of information besides the audio data. One type, relevant to the audio and embedded in the diagonal stripes, includes sampling rate, normal- vs. long-play modes, a copy-prohibit code, and a signal to align the heads with the recorded stripes. The second type is related to the tape rather than the audio content and is recorded in strips along the tape’s edges. The information in those strips—start, stop, and skip IDs; track numbers; and various date/time stamps—can be changed without affecting the recorded audio.
DAT’s Successes and Failures
DAT never achieved the commercial success with consumers that had been envisioned. Its technology was much more complex than that of cassettes, and the prices were commensurately higher. Periodic maintenance and repair added to the cost, whereas failing portable cassette recorders could be discarded and replaced with newer models with improved capabilities. Lastly, the number of albums released on DAT was comparatively small. Sony discontinued all DAT models in 2005 and ceased production of DAT tapes in 2015.
Where DAT did succeed was in recording studios. With the emergence of digital mixing consoles and multi-track recorders, DAT allowed content to remain digital everywhere from analogue-to-digital conversion of microphones’ signals to the CD or DAT player’s digital-to-analogue converter, and DAT decks could replace reel-to-reel tape recorders in creating stereo masters. This use of DAT, however, has fallen off due to the advent of direct-to-disc recording technologies. (While searching eBay for DAT decks, I noted several professional DAT decks that had been retired from studio use.)
DAT technology also found success in a different arena. Digital Data Storage (DDS), a variant of DAT, has been used for computer data storage, particularly for back-ups. While new DAT tapes are no longer being produced, new DDS tapes continue to be available.
Another factor will eventually end all uses of DAT and DDS. Like any other magnetic tape, DAT and DDS tapes are subject to deterioration due to age, environmental conditions, and improper handling.
I had never seriously considered acquiring a DAT player for my business, since I anticipated little demand. What changed my mind was a customer who wanted dozens of 60- and 120-minute DAT recordings converted to MP3 files, and the projected income from that project would cover the cost of a DAT deck. I can now provide DAT conversion services in addition to conversion of other tape and record formats. I do have lingering concerns: finding someone competent in DAT repair and maintenance who is willing to do the work, and the availability of replacement parts. (None of the devices pictured in Figures 3 and 4 are functional, and every repair shop I contacted declined to work on them.)
DAT Devices
Decks: DAT decks have been used by audio enthusiasts and in recording studios (Figures 1 and 2). Their 17” width matches the common breadth of amplifiers, cassette decks, CD and DVD players, VCRs, et al. and were intended to sit on a shelf. Those destined for studios have mounting brackets extending from either side of the front plate, which allows decks to be bolted into equipment racks.
DAT decks typically have several balanced and unbalanced analogue input and output jacks, allowing connections to a variety of other devices depending on the user’s or studio’s needs. Balanced connectors have an additional wire that carries the same signal as the one that will be recorded or played except that the phase is reversed; this eliminates electronic interference that may be induced in a long cable (the large circular “XLR” ports in Figure 2). The unbalanced analogue connections are the small red and white “RCA” jacks, ubiquitous in audio equipment. Decks also had balanced (XLR) and coaxial (orange) digital input and output ports. The standards for digital audio transmission changed over time, and I was never convinced that connecting a deck’s digital output to my amplifier would work. Fortunately, I was able to connect my DAT deck to my amplifier using a pair of analogue XLR cables, though RCA cables would also have worked.
Figure 1. Tascam DA-30 DAT deck (1990) playing a tape.
Figure 2. Back of Tascam DA-30 DAT deck.
Personal Portable Recorders: Personal portable DAT recorders have many of the capabilities that decks have but packaged in a case about the same size as a portable cassette player. Sony’s first DAT Walkman was introduced in 1990, and ensuing models were issued until DAT devices were discontinued in 2005. Pictured in Figure 3 are a Denon DTR-80 (early 2000s) and a Sony PCM-M1 (2004).
Both recorders have Line-In and Line-Out jacks for connecting the recorder to another device. But unlike decks’ use of XLR and RCA jacks, they have a single 3.5 mm stereo jack commonly found in portable devices. Connection to components other than portable devices requires an adapter.
Figure 3. Denon DTR-80P and Sony PCM-M1 personal portable DAT recorders.
Professional Portable Recorders: Professional portable DAT recorders occupied a position between decks and personal portable recorders. They were larger and heavier than personal devices, but small enough to be carried around, albeit in a case big enough for the recorder, spare tapes and batteries, a charging unit, two microphones with their cables and stands, et al.—definitely not something one could clip to one’s belt. The Tascam DA-P1 pictured in Figure 4 measures 9¾“ x 7½“ x 21/8“. Heftier tape transport and head mechanisms and electronics require more electrical current to function, and this is reflected in the size of the rechargeable battery (6½“ x 15/8“ x 7/8“, also appearing in Figure 4).
The input and output jacks are shown on the side of the unit. They include, from left to right, coaxial digital input and output jacks (orange), analogue Line-In and Line-Out RCA jacks (red and white), and a pair of XLR jacks for microphones (the large round ones). While professional portable recorders omitted some of the input and output capabilities found in decks, what they had proved adequate for their intended use, connecting directly to more audio devices than permitted by 3.5 mm stereo jacks and avoiding the need for an adapter.
Figure 4. Tascam DA-P1 professional portable DAT recorder and its battery.
Cassettes: Both cassettes and DAT tapes use 3.81 mm tape (commonly referred to as 4 mm), and their spools are housed in plastic cases (see Figure 5). While cassettes have openings along one edge where the tape makes contact with the player’s heads, DAT tape cases have hinged lids that protect the tape (the player moves the lid out of the way when the cassette is loaded). Common cassette tape lengths are 60, 90, and 120 minutes (half on each side), and common DAT tape lengths are 60 and 120 minutes (DAT records in one direction only). Longer tapes have been made for both formats (e.g., 180 minutes), but such tapes are more likely to stretch or break because of their thinness. (Due to the diagonal stripe pattern of information on a DAT tape, it is impossible to edit a tape by cutting and splicing or to splice a broken tape). Long cassette tapes are also more susceptible to print-through, where magnetization bleeds into adjacent layers of tape on the spools, usually resulting in pre-echo.
