Nibble 35 - Digitizing the Cassette Tape - Digital Audio Tape and the Digital Compact Cassette

When the average Joe was introduced to digital sound recording through the Compact Disc in 1982 it caused a revelation. Clear and perfect sound reproduction, free from the “pops,” scratches, and hiss from records and tapes. It convinced some to throw away their record collections (to the dismay to some this century). But the CD was not fully perfect. Unlike cassette tapes, CDs can’t fit in a pocket and (until CD burners came in the 1990s) could not record. If someone wanted to make a playlist from tracks in their CD collection, the only means to do so was tape. And that tape was analogue. Making a digital version of tape was a logical next step. However, as the cassette tape was getting digitized, the recording industry was getting concerned over the perfect copying possible with digital formats and how that could hinder record sales. Music piracy was a concern when cassette tapes were analogue, but their analogue nature did offer some comfort that it didn’t copy things perfectly – unlike digital. Because of privacy paranoia in the record industry, the digital cassette tape was hindered from becoming a successful replacement of the analogue cassette. Analogue tape remained the medium for mixtapes until MiniDisc and writable CDs came along. Since then, the digital cassette tape has become a tech curiosity. The digital cassette tape (mostly) came in two forms – the Digital Audio Tape (DAT), introduced by Sony in 1987, and the Digital Compact Cassette (DCC), introduced by Philips and Matsushita in 1992.

“Now that Compact Discs, with their scratch-free, brilliant digital sound, are the home-music standard, Sony and Philips are fighting fiercely over portable digital audio systems.” – David Elrich (New York magazine, 1993)

Digitizing Tape

The digitalization of audio tape began in 1967, when broadcaster NHK developed the first mono pulse-code-modulator (PCM), which converted sound into digital data that was then recorded onto video tape. They developed a stereo version in 1969. This was used to make the first commercial digital recordings in 1971. The engineer that headed these developments, Heitaro Nakajima, left NHK and joined Sony in 1971. He played a big role in developing the Compact Disc.

The average Joe first got their hands on digital tape in 1977, when Sony introduced the PCM-1 Audio unit, the first consumer PCM adaptor, which turned a VCR into a digital tape recorder. In 1981 Technics took this a stage further by combining the PCM and a VCR into a single unit, in the form of the SV-P100 Digital Cassette Recorder. Limited to bulky video cassettes (in Technics case, VHS), digital tape wasn’t really portable, like the analogue Compact Cassette. So, digital tape remained in the use of professionals and audiophiles with money. Nothing for the Recording Industry to worry about … let.

One name that comes up when searching for the inventor of digital audio tape is scientist Thomas Stockham. He developed his own digital tape-recording system and founded America’s first commercial digital recording company, Soundstream, in 1975. Soundstream were the first to computerized sound editing, and used that tech to do the first ever digital restoration of a recording. This leads to many accidently crediting him with the DAT format. But this author can’t find any evidence that he ever worked with Sony, let alone worked in developing the DAT format.

Digital Audio Tape (DAT)

As soon as the Compact Disc went on sale, manufacturers began work on a digital cassette tape. They were many incompatible prototypes made. In 1984 representatives from 81 companies met in Japan to establish standards for digital cassettes. The DAT standards committee was chaired by Heitaro Nakajima, who left Sony in 1983 and later became president of Aiwa, who released the first consumer DAT deck. In 1986 the Electronics Industries Association of Japan (EIAJ) released specifications for two formats – S-DAT (stationary-head digital audio tape) and R-DAT (rotating-head digital audio tape).

Sony started work on DAT in the late-1970s, with several engineering teams taking different approaches to the technology. In 1981 a S-DAT prototype was announced. In 1982 Sony unveiled a prototype for a R-DAT. Both were developed, with the S-DAT later becoming the NT format in 1992. In the January 1986 CES show, in Las Vegas, Onkyo (one of Sony’s DAT partners) revealed (behind curtains) their prototype DT-1000 DAT recorder. Why the curtains? Because, according to Tom Yoda, president of Sansui Electronics, “People are having enough trouble absorbing the new technologies of compact discs, laser video discs, VCRs, camcorders, and more. Once the compact disc has firmly established itself, that will be the time to introduce DAT.” Introducing DAT early would hurt the sales of other devices. This fear delayed the introduction of DAT and made manufacturers keep quiet about their work on it. … until it was finally DAT demonstrated at the Japan Audio Show in October 1986 and finally launched in Japan on 2^nd March 1987.

The first consumer DAT deck was the Aiwa Excelia XD-001. Released in Japan on 2nd March 1987, it sold for 188,000 Yen (about $1,225). It was the first component of Aiwa’s Excelia series of digital-to-digital audio components.

Born – 2nd March 1987

Size – 73 mm × 54 mm × 10.5 mm

Tape Width – 3.81mm (0.15 inch)

Default Tape Speed – 8.15 mm/s (3.208656 in/s)

Max. Sound Quality – 48kHz, 16-bit

Price of Blank Tapes at launch – 1,400 Yen/$9 (for 60 minutes), 2,000 Yen/$13 (for 120 minutes)

Max. Poss. Record Length – 180 minutes

The DAT cassette is smaller than a Compact Cassette. It was considered great for consumers, meaning smaller devices, but professionals thought it was too small.

Initially, alinement problems made playing a tape recorded from one machine in another sometimes impossible.

The record/playback heads in DAT players are 50% wider than the tracks they record.

Unlike the break-away notches on Compact Cassettes, DATs use a slider to enable/disable recording.

“If we were to go with a stationary-head approach, we’d have to come up with new tape-head technology and better tape formulations, … That would result in a mush costlier DAT recorder for home use. It might be so expensive that no one would want to buy one. … The industry has gained a lot of experience with precision fast-spinning tape-head drums in VCRS, and this experience can be put to use with R-DAT machines.” – Almon Clegg, engineer from Matsushita Electric Corp. of America (1986)

Recording on DAT

The DAT player is like a miniature VCR. Inside a DAT player is a 30mm diameter rotating drum (angled at 6° 22’ 59.5”), containing two (or four) record/playback heads. These heads are azimuth angled 20° from the tape to create destructive interference if two tracks are accidently read, allowing tracks to be placed closer together on the tape. This drum rotates at 2000 rpm (mostly). With the going pass it at 8.15mm/s, the rotation gives it play-heads a total writing speed of 3.133 m/s (123 in/s – 65 times faster than a Compact Cassette’s tape. This results in data recorded as diagonal tracks 13.591µm wide and 23.5mm long.

Each track is up of 196 blocks, each 288 bits long, totalling 56,448 bits – or just over 7KB. It is divided into 16 sections, as shown below.

Subcode encodes additional information about the recording, such as its timecode and Start/Skip IDs.

Automatic Track Following (ATF) data tells the player if it is playing the correct track are here.

Phase-Lock Loop (PLL) Signals used to check if data is in sync.

Each block is made up of 8 synchronisation bits, an 8-bit identification word, an 8-bit block address word, an 8-bit parity word, and 256 bits of actual data.

Record Modes

DAT’s default standard mode for recording is 2-channel, 16-bit, 48kHz. The EIAJ committee chose this sample rate to make it incompatible with CDs. Pre-recorded tapes were recorded at a sample rate of 44.1kHz, the same as CDs. Some recorders were able to record at this sample rate, streamlining the CD mastering process. There is also a 12-bit 32kHz mode, compatable with satellite broadcasting. It can in stereo or quadraphonic.

In duplicating tapes, the tracks can be made wider to increase reliability and speed of production – at the cost of reduced maximum recording time.

The Music Industry’s Assassin?

When the Compact Cassette appeared the record industry ignored it, due to its initial low quality sound reproduction. But that improved over time, and by the 1980s it was crying “Home Taping Kills Music.” The coming of DAT’s perfect digital reproduction capabilities alarmed the industry.

Stanley Gortikov, president of the Recording Industry Association of America, wrote two “open letters to Japan” in Billboard magazine ranting about it. One started like this - “An “assassination” is in the making. The targeted victim is the world’s music industry. The assailants are Japan’s equipment makers. The chosen weapon is DAT – digital audio tape.”

So, the record industry acted pre-emptively, and tried to get DAT banned by suing Japanese manufacturers. As Japan was facing a number of attacks from the US over various trade issues, mostly due to a stronger Yen compared to the US Dollar then, the issue forced them to delay the launch of DAT in America.

Copy Code

CBS Records tried to solve the issue by developing a copy protection method called Copy Code. In this system, recordings contain an audio signal detected by a chip in the player. If the chip detects no signal, due to it been a copy, it shuts down the recording function. Unfortunately, the code proved auditable, especially in classical music. Many record producers and classical artist opposed Copy Code, as it would distort their work, when the US House of Representatives considered a trade-bill amendment (the Digital Audio Recorder Copycode Act of 1987) mandating it in all DAT machines. After the National Bureau of Standards tested the system, and found the code auditable, the bill was dropped in 1988.

Meanwhile in Europe

In Europe, the EEC originally favoured adding Copy Code to DAT machines sold in Europe, but after a demonstration in London, experts called out its audibility, leading to them changing their minds, and recommending member countries to do so. Relieved, Sony unveiled the DAT format at the 1987 Berlin Audio Fair and announced its sales in Europe will begin in October 1987.

Getting DAT Early

For a while, the only way Americans could get their hands on a DAT recorder was through the grey market import route. But a few in the US were impatient … or just wanted publicity. In June 1987, as a “grandstand play,” Marantz announced plans to introduce America’s first consumer DAT recorder, without Copy Code, in October 1987. But the political turmoil made Japanese suppliers reluctant to build the machines. In January 1988, non-recording DAT players for cars were introduced to the US. In March 1988, Marantz announced their plan to introduce their recorder in June, but again the suppliers refused to build them. It is listed in Stereo Review’s Stereo Buyers’ Guide in 1989. After a few false starts, the Marantz DT-84 finally went on sale, for $1,900, in 1990.

Serial Copy Management System (SCMS)

An alternative Copy Code was devised, which actually worked. Philips developed the Serial Copy Management System (SCMS). It uses two bits in the audio stream to indicate if a recording was “protected,” “unprotected,” “original,” or a “copy.” If one recorded “protected original” material form a CD or pre-recorded DCC, the resulting tape’s audio will be marked a “protected copy.” If one tried to record such a “protected copy” the record button won’t work and any ongoing recording would stop, and an error message would appear on the display. “unprotected” recordings are free to copy. Recordings from analogue sources are marked “unprotected.”

After a meeting in Athens in 1989, manufacturers and the music industry approved SCMS. Thanks to all this, American consumers didn’t really get hold of DAT recorders until “DAT Day” – 22nd June 1990. But it didn’t stop all the critics. In July 1990 Songwriter Sammy Cahn and four music publishers filed a lawsuit seeking to block Sony from selling DAT, due to the lack of royalties’ provisions in the Athens agreement. To drop the suit, in 1991 Sony agreed to support legislation creating a royalty scheme for digital media - the Audio Home Recordings Act of 1992. This made it mandatory for all “digital audio recording devices” to use SCMS, including DAT and (later) DCC machines. However, manufacturers lobbied to limit the use of SCMS to audio recorders, and not computer storage devices. This, fittingly, made the later digital music piracy boom, bought on by CD burners and file-sharing (and not DAT, as the record industry thought it would), possible. This was proven fact when the RIAA tried to sue Diamond Multimedia System, for making the first MP3 player, in 1998. Because MP3 players can be used store any form of data, and not just audio files ripped from CDs or downloaded for the internet, they are exempted from requiring SCMS.

The reality that record companies didn’t realise is that dubbing a CD onto a DAT can only be done IN REAL TIME. Even if the most patient of pirates, the fact remains that the copies can only be played on EXPENSIVE DAT players. Not exactly the pirate-friendly format the record industry thought it was.

Music on DAT

The first pre-recorded DAT tape was The Durutti Column’s The Guitar And Other Machines, released in December 1987. It was mostly smaller record companies, like Factory Records, that released music on DATs. The larger companies mostly refused due to piracy concerns.

At 7:30 p.m. 31^st May 1987, WFMT radio in Chicago made North America`s, and probably the world`s, first broadcast of audio from a DAT. Telarc and DMP provided the pre-recorded tapes of classical music and jazz, and Sony provided a DTC-1000ES player.

The Sony DTC-1000ES is the first DAT recorder sold in Europe, retailing in the UK for about £1,000. It looks like the Aiwa Excelia XD-001 because they are the same machine, except the faceplate.

DAT - A Minor Success

DAT was a bit successful, despite little consumer adoption, due to its price. It was mostly used by professionals in the record industry (to record masters for pressing CDs, ironically) and IT as a data storage medium, mostly in the form of the format Digital Data Storage (DDS). Eventually, hard drives and flash memory replaced DAT. Sony introduced their last DAT player model (the TCD-D100 DAT Walkman (Yes, they made Walkmans that used DATs.)) in 1997 and made their last ever DAT recorder in 2005.

Digital Data Storage (DDS)

Introduced in 1989, a 90-metre tape initially was able to store 4GB uncompressed. This improved over time, eventually leading to a 154-metre tape been able to store 80 GB uncompressed in 2007. But these improvements made tapes between generations of drives incompatible.

Digital Compact Cassette (DCC)

“How to hear the future without giving up the past” – 1993 press ad

Initially referred to as S-DAT (Stationary head Digital Audio Tape), the Digital Compact Cassette was developed by Philips and Matsushita. Designed by Peter Doodson (of CD jewel case fame), the DCC is a true reinvention of the cassette tape. The tape is protected by a floppy disk-style slider. Players have auto-reverse as a standard feature, meaning only side need holes for the sprockets, leaving the other side free for a large label. And then there is the fact that players can also play Compact Cassettes too, making them backwards compatible. DCC was officially introduced at the Consumer Electronics Show, in Chicago, in May 1992 and the Firato Consumer Electronics Show in Amsterdam in September 1992. It was first sold in Japan 21^st September 1992.

“… There is no question that it rivals CD sound quality …” – Stereo Review, November 1992

Born – 21^st September 1992

Size – 100mm × 64mm × 9.6mm

Tape Width – 3.81mm (0.15 inch)

Tape Speed – 17/8 inches per second (4.76 cm/s)

Max. Sound Quality – 48kHz, 16-bit

Price of Tapes in 1993 – $9 (75-minute blank), $10 (90-minute blank), $16 (pre-recorded)

Max. Poss. Record Length – 105 minutes (120 minutes tapes were talked about, but never released)

The first DCC player was the Philips DCC 900. It sold for £499 in October 1992.

Backwards Compatibility

“Finally, an invention that doesn’t force you to buy the Beatles’ White Album for the sixth time.” – David Elrich (New York magazine, 1993)

DCC players can play analogue Compact Cassettes. Philips hope this would aid adoption of the new format by people who have pre-existing tape collections. It also meant that the players can be cheaper than DAT players, using modified Compact Cassette mechanisms, instead of all new one.

DCCs have several extra holes and indentations than Compact Cassettes for players to identify it is a DCC and what length it is.

Unlike the break-away notches on Compact Cassettes, DCCs use a slider to enable/disable recording.

Single-sided?

Like on Compact Cassettes, the tape is split into two “sectors.” However, DCCs are single-sided in design, with hub holes only on one side. It doesn’t need holes on the other side, because auto-reverse is a standard feature on ALL DCC players. With no need for holes, one side can be completely flat and be occupied by a large label.

DCC Tape

The tape in a DCC is the same width to that used in Compact Cassettes. The tape in production cassettes was the same as used in video cassettes - 12 µm thick, with a 3-4 µm thick layer of chromium dioxide or cobalt-doped ferric-oxide. Recorded on each “sector” (side) are eight audio tracks and a ninth “auxiliary” track for information.

Record/Playback-Head

The “combihead” play-head in stationary DCC players has nine narrow heads to play the digital tracks and two wider heads to play analogue cassettes. As all players have auto-reverse, the head rotates to play the other side of the cassette. But this mechanism was too bulky for use in portable players. So, in portable playback-only players the static head has 18 heads, 9 for each side. Two of these heads are used when playing an analogue cassette. In portable recorders the head contains 40 heads, 18 for recording, 18 for playing DCC and four for playing analogue tapes.

A spring-loaded metal slider covers the tape access holes and lock the hubs while the cassette is not in use.

Data is recorded (using 8-10 modulation) on the eight audio tracks in the form of “tape frames,” each made up of 32, 510-bit (51 “bytes”) long, “tape blocks.”

Each block is made up of a “header” and a “body.” The header is made up of three “bytes,” making up a 10-bit sync word, and two bytes made up of a 3-bit frame address and a 5-bit block address. The body, containing the actual audio data, is 48 “bytes” long.

Frame Address counts the tape frames on a tape

Block Address counts the blocks within a tape frame

On the Aux track, data is recorded in four tape block-long “Aux data tape frames.” It’s also made up of a “header” and a “body.” It doesn’t have to be inline with the audio tracks.

The gap between tape frames varies in length, depending on the audio sampling frequency of the recording.

Error Correction

According to Philips, using Reed-Solomon error correction, a DCC player can recover all missing data off a tape, even if one of the 8 audio tracks were completely unreadable or if all tracks were unreadable for 1.45mm (about 0.03 seconds).

Data Compression

DCC uses a data encoding system called Precision Adaptive Sub-band Coding (PASC). Like the MP3 file format, this system reduces the amount of data needed to store a recording by removing sounds the human ear can’t detect. Philips claim that, with PASC a DCC uses only 25% of the bits needed for a CD recording.

Auxiliary Track

DCCs came in three forms, although they look pretty much the same externally. The only main difference is what they record on the 9^th auxiliary track on the tape.

Pre-recorded tapes have all the album’s information (artist name, track titles and lengths, etc) recorded on the 9^th track continuously throughout the tape, making the info accessible, even if the tape wasn’t rewound.

Blank “user tapes” have track markers recorded at the beginning of every track. They are automatically added when silence was detected during an analogue recording, or a track marker is detected in a digital recording. These markers can be modified afterward to “merge/split tracks.” Other markers can be added to tell the player that a recording has ended and stop, or fast forward to the end and play the other side.

Later on, “super user tapes” allowed users to enter their own title information for each track. This data was recorded on the 9^th track after the start-of-track marker, making the info inaccessible sometimes.

Packaging

DCC tapes were packaged differently to Compact Cassettes, but their overall dimensions were almost the same as a Compact Cassette case. Pre-recorded tapes are slid in and out the side of a simple plastic box with a window, which revealed the tape’s label. Panasonic made blank tapes packaged in a clamshell-style case. As the tapes didn’t have the bulge that Compact Cassettes had, there was more room in the case for a leaflet or note card.

Music on DCC

“All six major record labels are putting out music of DCC, …. There will be about 500 pre-recorded titles available in September [1992] when the [first] unit is marketed. This is a crucial part of the DCC appeal. History has shown that any new technology, without software support, tends to fail.” – Mike Piehl, marketing manager of Philips’ audio division

On its launch, PolyGram started shipping over 100 pre-recorded titles on DCC. Among those who first appeared on DCC were Bryan Adams, Prince, Frank Sinatra, Georg Solti, U2, and Luciano Pavarotti.

Competing with DAT

Compared to DAT, DCC was widely supported by the record industry. Additionally, the DCC format allowed the duplication of tapes at 64 times normal playing speed, making pre-recorded tapes cheaper than DATs, which can’t bet duplicated fast. The possibility of DAT and DCC entering a Beta vs VHS style format war was played down by Philips. They considered DCC a “niche” product. Guy J. Demuynck, vice president of audio marketing at Philips’ American branch, said “In fact, DAT may very well become the digital equivalent of the reel-to-reel tape recorder of the 1970s, serving that top segment of the market.”

Success?

DCC was marketed in Europe, the US and Japan. In some places in Europe, it proved more popular than MiniDisc, especially in Philips’ homeland of the Netherlands. But, in the end, DCC was too expensive for the youth market Philips aimed for. Audiophiles didn’t like its lossy compression. After poor sales, Philips discontinued DCC in 1996.

Unspooled Failure

The digitized cassette tape proved to be a pointless creation in the end. DAT and DCC were too expensive to consumers and few saw the point of them, while most were fine with analogue cassettes. In the end, the MiniDisc and (later) the writable CD provided the consumer’s need for a recordable digital audio format. Tape, period, was old news. As David Elrich of New York magazine said in 1993 “trend-surfers know that tapes simply aren’t cool anymore.”

“Shortly before the launch of MiniDisc, and Digital Compact Cassette, in the UK, I was at an event where they were both been demonstrated, one after another. The representative from Sony got up, demonstrated the MiniDisc, showed the machine, … And then the Philips guy got up and did the same thing. It was all going fine for both of them …. everyone was quite impressed. Until the Philips guy decided to skip to a certain track. At that point the tape started winding on … everyone was sitting in the room listening to this thing going [woosh] moving its way through the tape. And an audible giggle starts up in the room. People were actually laughing at it, because, at that point, Digital Compact Cassette just looked like old technology that had been tarted up, whereas the MiniDisc looked a little like something someone had bought back from the future.” – Techmoan, MiniDisc - An Appreciation (2017)

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Nibble 35 - Digitizing the Cassette Tape - Digital Audio Tape and the Digital Compact Cassette

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