PRAISE OF THE FORMAT: COMPACT DISC

lthough the word "digital" in reference to the word "sound" is associated with our modern times, this combination has a much longer history. Research on a transfer of digital audio signal began in the 1930s at Bell Labs. This company developed the digital signal coding known as Digital Pulse-Code Modulation (PCM). As you can guess, it was intended for telephone signal transmission.

The beginning

The Compact Disc has a diameter of 120 mm and can hold up to 80 minutes of music material. The lower side, as presented in the photo, reflects light - it is an aluminum protected by a layer of poly-carbonate

This invention was first commercially used in the 1940s, during the Second World War. Bell Labs engineers developed a system called SIGSALY, which encrypted conversations between London and the Pentagon as an analogue transmission could have been easily intercepted by the Nazis. SIGSALY was not broken and was used until 1946. But it was declassified only in 1976 (Thomas Fine, The Dawn of Commercial Digital Recording, „ARSC Journal” 2008, vol. 39, No. 1).

From a technical point of view, that did not matter anymore, because the work on digital sound recording – not only transmission – was being done since 1960s. Although the PCM encoding originated in the United States, the first successful attempt to record such a signal was performed in Japan and again it was not music-related, but intended for use in television. The Technical Research Laboratory engineers, which was a research facility of the state owned NHK television network, already in 1968 built a prototype of a monophonic recorder, and in 1969 they already had a two-channel model. The NHK system sampled signal at 32 kHz with 13-bit resolution (Thomas Fine, p. 3; according to voices.com it was invented in 1967, and it was a 12-bit recorder, more HERE, accessed on June 16th 2017).

Number of tracks and their lengths - so called TOC – are encoded on a small strip in the center of the disc; even closer to the center additional information is encoded, such as the record label or disc type - as in this case.

To record the signal a video recorder was used – a reel-to-reel tape recorder utilizing a helical scan. To convert signal to a form acceptable for recorders special adapters with A/D and D/A converters had to be used. The idea to use video recorders to record digital signal was so successful that it became a standard for the whole industry for many years. The most commonly used recorders were made by Sony – especially models such as 1600, 1610 and 1630 which used U-Matic ¾ magnetic tape. Later these were replaced by DAT tape and then by CD-R and finally by file transfer.

Digital music for the first time

The first record label that used this revolutionary idea was the Nippon Columbia, outside of Japan known from the Denon brand. Already at the end of the 1960s, it was working with NHK engineers. Although from today's point of view it may seem strange, they were about eliminating the disadvantages of analogue tape and eventually improving the sound quality. Nobody talks about it, but analogue recording on tapes, even at 36 cm / s speed, is loaded with a lot of problems, such as high level of noise and relatively low dynamics, dropouts and rapid deterioration of treble quality over time. They tried to cope with these problems using noise reducers such as Dolby A and DBX, but these were only half-solutions.

In the 1990s in Japan digital singles or Mini CDs - 80 mm optical discs and of 210 MB capacity corresponding to 24 minutes of music - were very popular. Later they were also popularized in other countries, and in the 21st century they began to disappear from the market. On the photo one can see the single added to the special version of the Justyna Steczkowska Dziewczyna Szamana.

I would like you to see this moment in the right way: the Denon guys who were responsible for the return of direct-to-disc recordings, who had great funding at their disposal, who knew what a good sound was, were just looking for a way to improve the sound, they wanted something more. All that despite the fact that, as it seems, their analog recordings were among the best in the world at the time. So it was not the pursuit of novelty, nor a need to make some meaningless changes.

The only commercially available media for this type of recording was Long Play. This is an analog medium, so digital signal must have been firstly converted by, at the time discrete, D/A converter. In January 1971, the first "regular" (before that there were several test releases) release of Steve Marcus's digital recording, Something was released by Nippon Columbia under catalog number NCB-7003 (more about the early "LPs" in the article Digital technology in the world of analogue. Trojan horse or a necessity?, HF No. 155).

Digital music for the second time

Already at that time, however, it was obvious that the attempt to improve the parameters in the recording studio was only one half needed to success. Therefore research was launched to create a completely digital medium that would allow to utilize all the advantages of this type of recording. In 1974, the Philips research department combined optical reading and digital encoding to adapt the 30cm optical Analog Laser Disc intended to be used for analog video and audio recording, for digital audio.

Because some players were unable to play CD singles, same as most CD-ROM drives, publishers began to release them differently - although the laser reflecting area still had 80-mm diameter, the plastic part had a diameter of a classic CD. The photo presents the promotional single America by Bajm, released in 2003.

This was probably coincident, but in 1969, exactly when the Japanese had a working prototype of a digital recorder, Danish physicists, Klaas Compaan and Piet Kramer, working for Philips at the time, developed an analogue reading system that used a laser diode and optical techniques to read signal. In December 1972, the official presentation of the Philips Video Long Play (VLP) took place. In March 1979, the Dutch company presented a Compact Disc in Eindhoven.

This could have been a reason for a “war” of formats. Today it would happen with 99.99999% (7N) probability, but then the biggest rival of Philips, that worked on a very similar format, Sony, agreed to cooperate with Philips, and so the Compact Disc format, as we know it today, was born. Let's add that Sony was even more advanced in this research, since the work began in 1975, and a year later the official presentation of the results of this project took place. The official premiere of the Philips / Sony common format, described in a document called the Red Book, took place in 1982, although the first tests at the Polydor Pressing Operations plant were conducted a year earlier. The first CD released by Sony was Billy Joel's album 52nd Street.

Compact Disc

Today Compact Disc is obsolete, it's a symbol of the past era, at least in the eyes of young people. In the early 1980s, however, it was a cutting edge technology. Its popularity was initially hampered by the high price of CDs, but in the mid-1980s, the "digital revolution" sky rocketed and in 1988 the number of CD sold exceeded one of vinyl records. Based on this standard next ones were further developed: CD-ROM for computer data, recordable versions CD-R / RW and others.

CD format offers an option of storing information about album's and individual tracks' titles. Although CD Text has a nice logo, it is rarely used. The photo presents a re-edition of the Papa Dance Poniżej krytyki (remaster by my friend Damian Lipiński), which features the appropriate logo and the re-edition of the Polish Jazz album from 2017, where there is no logo, even though the disc includes information encoded in CD Text.

The Compact Disc is a disk with a diameter of 120 mm (4.75 ") and a thickness of 1.2 mm (0.005"). For some time also so-called "CD singles" were produced, or CD singles, with a diameter of 80 mm (3.1"). The CD is made of three layers: a transparent poly-carbonate (plastic), a reflective layer of metal and a transparent protective layer. Top surface of the disc can be covered with lacquer with information about the title.

The music signal is written on the metal layer in the form of pits (pit) and lands (flat area), which are digital equivalents of "1s" and "0s". The reading path is a spiral, starting in the inner part of the disc. There is also a so-called TOC, that is data about the number of tracks and their respective times. The centers of adjoining paths are just 1.6 μm apart. Initially, the discs could contain about 74 minutes of music. Later, after tightening the paths, it became possible to record up to 80 minutes on one disc.

CD reading is done with low-power laser. When the laser light illuminates the land (the flat surface), it is reflected and captured by the photo-diode, representing the digital "1". In turn when it falls to the pit, it is extinguished, representing the digital "0". This is because light reflected from the bottom of the pith, which has a depth of approximately ¼ of laser beam wavelength (0.78 μm), is not in phase in respect to the adjacent separation path. Such reflected light has a lower value than the minimum needed to activate the photo-diode.

Since a fixed linear read speed was chosen, the rotational speed of the disc varies depending on where the signal is read at a given moment and it ranges from 500 to 200 rpm, starting from the center. (more: britannica.com).

The digital signal recorded on Compact Discs is pulse-modulated – it is the same Pulse-Code Modulation, I mentioned earlier in this text. The signal is sampled at 44.1 kHz and the word length is 16 bits. Initially Philips preferred a higher sampling rate and a 14-bit word, but it was Sony's opinion that prevailed, because as the intermediary medium, ie the one used to send the material to the pressing plant, they suggested the U-matic tape, invented in the late 1960s for analog video signal recording. The audio signal was recorded on it with 16-bit words sampled at 44.1 kHz.

Post-Compact Disc

The HDCD discs were released by many audiophile labels, such as, for example, Audio Fidelity. The Deep Purple box includes HDCD gold discs.

The limitations of the CD format quickly came to light - both the word length and the sampling frequency. The first describes how precisely a given sample is described, and the other is how often samples are collected, also specifying the upper frequency response limit, that for CD is 22.05 kHz, and in practice it's about 20 kHz. It was not until 1995 that the solution of this issue was introduced - the High Definition Compatible Digital disc, that we know as HDCD.

This coding-decoding format, since 2000 owned by Microsoft, was developed between 1986 and 1991 by "Prof." Keith O. Johnson (now Reference Recordings and Spectral) and Michael “Pfash” Pflaumer for Pacific Microsonics so that, on a CD-like disc, playable on any CD Player, one could write a 20-bit word length (44.1 kHz) signal. A custom analog-to-digital converter was created to code the signal. To play this signal Player had to feature the appropriate circuit – the PMD100, which decoded the HDCD signal and worked as a digital filter - for this second feature it was also very appreciated also when using classic CDs.

The same year as the HDCD, another format was introduced, which, unlike the Pacific Microsonics' patent, became very popular: the DVD, the Digital Versatile Disc. This type of disc allowed to record digital video and digital audio signals. For audio the stereo and multi-channel signals coded in Dolby became standard, which was sometimes accompanied by a DTS encoded track.

Although the HDCD format seems to be dead commercially, still some HDCD releases appear on the market - the photo presents The Best of the Grateful Dead, that Rhino released in 2015.

The DVD allowed to record the audio signal alone, uncompressed, with 24 bits and 96 kHz resolution. A few companies, such as Chesky Records, benefited from it releasing a dozen or so titles called DAD - Digital Audio Disc. This simple method for selling high-definition signals (hi-res) was quickly forgotten when the first DVD-Audio disc hit the market in the 2000. The DVD-based disc allowed recording of a multi-channel 24/96 material and stereo 24/192 signals. To accommodate such a large amount of data, the signal was losslessly compressed using Meridian's MLP system. The extension of this idea is today the Blu-ray Audio.

None of these proposals, however, were widely accepted And it all changed when the era of high definition files began with PCM files with resolution up to 32 bits and 384 kHz and DSD up to DSD254 (more in this month’s editorial).

A STORY OF ONE ALBUM: Nat King Cole Love Songs

The CDs are the oldest digital, commercially used music medium. Their technical specifications make them the most “outdated” digital media we currently use. At the same time, however, the Compact Disc is still - in my opinion - one of the best if not simply the BEST audio medium, maybe apart from analogue tape and - under certain conditions - Super Audio CD. It does not mean that it will always be so - I assume that in the future files, especially in DSD format, will be the new "analogue". But not yet.

I have come to this opinion during years of contacts with all the known formats, both in the recording studio and in the home audio world. I have never accepted the fact of how much is lost when material from analog tape is transferred to vinyl record. Of course, the latter is a wonderful format, it offers a lot of joy, but it is only an approximation of what is stored on the master-tape. Music files? It's still an immature system that requires a lot of fixes on both sides, on the publisher's and on manufacturers of devices playing them in home audio systems.

Introduced in 1995, the eXtended Resolution Compact Disc (XRCD) incorporates a new mastering method, including analogue-to-digital transfer, and particular attention put on the way the glass matrix is made later used to press discs.

On the other hand the CD offers a sound quality comparable with any other format. The booklet included in the ABC (Int’l) Records releases reads:

Although we are great fans of DSD and vinyl records we believe that if your system is optimized for CD playback you should obtain better sonic results with CDs than with DSD and vinyl.

I'll get back to ABC in a moment.

Compact Disc, but a better one

This is all the more true that work is still being done to extract even more information from it. On the equipment side one needs to point out ever better digital-to-analog converters and ever better digital filters. Signal upsamplers also play an important role (see CD transport Chord Blu MkII). Yet, it's possible that even more important things are happening on the other side, of the compact discs.

In 1999, a change was introduced to the recording method of the signal for the pressing plant – for the first time a magneto-optic disc (MO) was used recorded on the Sony PCM-9000 recorder, which stored a 20-bit material.

The first attempts took place - this is the third time I mention this date – in 1995. The JVC (Victor Company of Japan, Ltd) presented the eXtended Resolution Compact Disc (XRCD). The XRCD includes both mastering and the method of pressing the disc. Mastering involves encoding an analog signal (later also digital one) in K2 encoder. K2 uses dithering, without resorting to noise shaping. The resulting 20-bit signal is recorded on a MO (Magneto-Optical) disc. This is, today a bit forgotten, Sony's format, combining the magnetic recording on a disc with its digital readout. MOs are very reliable over time, ie they do not change the recorded signal even over a long time. Later improved versions of XRCD have been developed called XRCD2 and XRCD24.

Even more interesting is what happens next with such material. The MO disc is then sent to Yokohama, to the JVC pressing plant and there up to 2000 copies are made from the glass matrix that is cut is such a way, that the pits have the greatest possible length. This number was determined experimentally based on matrix degradation results of listening to subsequent copies of the same disc. Do you remember what I wrote about the design of a compact disc? It turns out that the sound quality significantly depends on the precision with which pits and lands are made.

Another, for now the latest, version of XRCD is XRCD24; in this process the signal delivered to pressing plant is a 24 bit one.

This way we finally get to the discs we have already mentioned many times, ie Compact Discs, but prepared in a better way than before. The idea for their development came from the Crystal Disc, in which the plastic layer was replaced with a glass plate on which the pits and lands were etched, thus replacing the making of glass matrix and pressing the discs. The progress was so significant that Japanese companies, as we are still in Japan, devoted their time and money to finding a cheaper way to improve the pressing quality. Crystal discs cost between 60,000 and 100,000 Yen. That's how the Blu-spec CD and Blu-spec CD2 from Sony, HQCD (HiQuality CD) and UHQCD (Ultimate HiQuality CD) from Memory Tech and SHM-CD (Super High Material CD) and Platinum SHM-CD from JVC and Universal Music Japan (2008) came to life. More HERE.

These ideas come from reputable companies for which this part of their activity is nothing more than a small niche. And yet they decided to invest huge amounts of money in developing and promoting them, because they offer a real sound quality improvement. Why? The answer is quite simple, although it is not entirely clear why these particular changes actually affect the sound, theoretically they should not matter much.

The latest Japanese „invention” is the Ultimate HiQuality CD. Photo presents the special version of King Crimson's Radical Action…

It all comes down to the smallest possible interference to the signal when transferring it from the studio to the final customer. In classic cases, files are sent to pressing plant, where they are uploaded to a computer that controls the cutting of the glass matrix. At each of these stages, the signal changes. To eliminate the impact of the pressing on the disc, all the above listed formats instead of poly-carbonate, a synthetic resin, use a photo-polymer used in the LCD displays. It is more transparent, but even more important is the fact that after it is poured onto the surface and treated with light of specific wavelength, it hardens almost immediately, perfectly filling the matrix. The poly-carbonate needs more time to solidify, thus filling it with less accuracy.

AAD: Almost Analogue Digital

The Chinese company ABC used to release K2 discs prepared by JVC – photo presents the Joan Baez Diamonds and Trust… – but now it uses new technique, the HD Mastering, disc prepared in Germany – Western Electric album and sampler prepared for Japanese „MJ Audio Technical”.

This is how we return to ABC (Int'l) Records. It is one of the most interesting labels, and one of the youngest ones, founded in 2002. It is particularly interesting because it is a Chinese firm. They began pressing of disc in cooperation with JVC – these were discs in K2 format (20 bit Super Coding). Interestingly, neither on the disc nor in the printing included in the release one can find information on the fact that the album was pressed in Japan. The next step was establishing cooperation with the German Golden Ear Studio. Together, they developed a method of producing CDs similar to Japanese ones, ie poly-carbonate was replaced with "High Transparent Material" used for the production of liquid crystal displays. In addition, the lower layer, which in UHQCD and SHM-CD was a classic one, was modified here to better dampen the vibration (New High Damping Coating CD). These discs were named HD-Mastering CDs.

The results were excellent, but it still wasn't enough for the ABC. I did not mention that, but for pressing HD Mastering discs they used Master CD-Rs that were digital copies of analogue master-tapes. The music material was not mastered, i.e. no compression or limiter was used. The next step was inevitable: the sale of Master CD-Rs. Since these are real-time copies made directly from the analog master-tapes they are expensive.

The AAD disc come in sealed, carton boxes.

The source is a modified Studer A80 tape recorder, and the discs are burned on a modified HHB CDR-830 studio recorder. Copies are made on CD-R HHB or Quantegy CDR gold discs. This is discs intended to supposedly store data even for 300 years (nobody checked it obviously). Such discs come in a cardboard box embossed with logos and names, common for discs. Inside one finds a CD-R in a special stiff “socket”, a catalog and a certificate - each copy is checked for block errors - the assumed value is 3, while the industry standard is 200. The signal from the tape is converted using EMM Labs ADC 8 MkIV converter.

When I first heard such album, it was Nat 'King' Cole's Love Songs compilation, I was stunned (Int'l Records AAD-245A, Master CD-R, 2015). I know what quality to expect from Master CD-R disc, but almost always these are copies from digital “Master” files, and here this was a copy from the analog master-tape. The sound has an unbelievable energy, large scale, flawless resolution, and above all, it's amazingly natural. Songs compared to the various releases proved that the ABC version sounded much better even than the excellent mono version prepared by Analogue Productions. The stereo versions of the latter present voice in a sharp way.

The energy of which I speak is the key to understanding the whole presentation. The amount of information is so big that it saturates the sound so that it almost vibrates. It's not about sound distortion, but about almost supernatural credibility - I've never heard Cole's voice in such a way before. And yet, differentiation is better than on classic releases, except maybe for the best Platinum SHM-CD and Crystal Disc ones. Changes in the recording technique between individual tracks (this is a compilation album) and individual masters are clearly audible. I perceived them as changes, not errors. Listening to this release I wasn't looking for any problems but rather looking forward to the next track. Compared with Master CD-R, the classic releases sounds gray and lifeless.

Simply: Compact Disc

The Compact Disc format is celebrating its 35th anniversary this year. It had enough time to mature and from a popular media to grow into a high-end carrier. What helped this process was a change the professionals approached digital signal, freeing themselves from limitations of purely technical approach, and taking advantage of research conducted both in universities and in research departments of many companies. This is currently the most reliable audio format available. Of course, one must has the right player at one's disposal and high-end releases, same is the case in the analog world. Unlike vinyl, usually the first releases are not the best ones, but rather the special ones. And at the very top there are Master CD-Rs and Crystal Discs.