From it's inception, compact disc has gone from strength to strength and is now the most common of the many formats currently available.  

As the first consumer digital format, compact disc is a good way of storing music. The audio signal is stored in the form of a number code which can be played back with a wide dynamic range and negligible background noise. CD first became available in 1983 and was a joint project from Sony and Philips.  CD was at the cutting edge of technology and compromises had to be made to get it to work. These compromises were in resolution (i.e. the accuracy of the translation from audio signal to digital code) and in cut-off frequency (i.e. the highest frequency of sound that is recorded).

Rightly, or wrongly CD is generally regarded by the masses as being the ultimate in sound reproduction. The initial promise of 'perfect sound for ever' was a bit excessive. The claim was based on the ruggedness and stability of the disc and the fact that if there was any damage, it could be corrected using computer techniques. Since those heady days, it has been found that the discs can deteriorate and that the error correcting process can affect the sound. Modern high-quality cd players recognize the shortcomings of cd and overcome them to give the best possible sound.

Over the years the technology of cd players has steadily improved to the extent that the limitations of the original recording are now seen to be holding back progress towards ultimate sound quality. Various alternative formats are fighting for the market at the moment and there is no clear front runner. Many HiFi manufacturers currently support HDCD^® which is an enhanced cd format and is already established in the audiophile market.   However, regardless of  what you may read in the hifi press standard 'red-book' cds are now too well established to disappear overnight - they've still got plenty of years left in them. You won't go wrong with a high-quality cd player even if another format does come along.

Unlike the analog format of the old-fashioned LP record, in which a stylus traces a groove pressed into the record's surface, a CD player retrieves data by shining a focused laser beam on the underside of the disc. Because nothing except light touches the disc, playing a CD causes no more wear to the recording than reading does to the words printed on this page. Furthermore, the audio quality of a CD is extremely high, and any part of the disc can be accessed quickly for playback.

When music is recorded digitally, sound is sampled and represented as a series of numbers that measure the amplitude of the source signal. Thousands of numbers are needed to describe even a brief sound. These numbers are encoded in binary form (as strings of 0s and 1s) and stored in the form of microscopic pits and smooth areas called lands on the disc's data surface. During playback, the CD player's laser light reflects back from the rotating disc at varying intensities as it strikes the pits and lands. A photodiode array detects these fluctuations, which are then translated into 0s and 1s. This binary stream is decoded through demodulation and error correction and converted back into a variable electric signal, which is amplified and played through headphones or loudspeakers.

 



The groundbreaking 'Sony CDP101' - The First of many. 

 

 

Their small size (5" Inches diameter) and capability to withstand reasonably rough handling has meant that they have been adopted into all aspects of audio equipment from separates, full systems (mini; midi; micro etc.) to portables, in-car audio and personal CD players.

Compact Disc players offer significant advantages in sound quality over previous analogue components for several reasons.

1. The optical readout and digital signal processing techniques produce exceptionally accurate audio signals, so there is no wow or flutter, no rumble, no tape to stretch and no vinyl to scratch.
2. The laser beam that tracks the discs cannot wear or scratch the information contained on the CD.
3. The optical read out achieves a level of accuracy that no mechanical system could ever achieve.  
4. Due to the laser beam being highly convergent and most CD player having error correction circuitry, most particles of dust and small scratches on the CD itself aren't read, so they don't affect the sound quality

 

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Compact Disc and it's implementation in my system.

As one would expect Compact Disc is currently employed in my system as the primary source.   I am very lucky in having a pick of equipment for use in the playback of compact discs.

My compact disc player of choice is a Naim CD3.5 which upon purchasing, surpassed all my previous expectations from the CD format.   The Naim is used as my main listening source.

In addition to the Naim, I am also the proud owner of a ROTEL Transport & DAC (Digital-Analogue Converter) combination.   The ROTEL CDP (Transport/DAC) forms the basis of my digital recording system and as such, nearly all my digital equipment is operated through it, DVD being the only exception.  

Other compact disc components that are in everyday use are a  PIONEER PDR-04 CD Recorder and a Pioneer DV717 DVD Player.

 

My player of choice - The Naim CD3.5  

"More Balls than the England football squad" -   KeVlaR 2000

 

 

In the paragraphs above, I mentioned a Transport and DAC being used in my system.  Exactly what is that and what is it's role?

Just as with a separate pre-amp and power amp, a separate cd transport and digital to analogue converter (DAC) will reduce interference between the two units and stop any power fluctuations in one having any effect on the other. Furthermore, because there is more space available in the box, the designers are free to use better quality components and a better circuit layout. The very best digital to analogue converters produce extremely musical, accurate and real sound.

Another advantage is that a separate DAC usually has multiple inputs, so you can use it to enhance the quality of other digital formats such as MiniDisc, DVD, DAT and even some PC soundcards which have digital outputs.

If you already have a high-quality CD player with a digital output, then the addition of a separate DAC is an excellent upgrade. With such a setup, your system is also future-proof, because you can upgrade either the transport mechanism or the DAC to keep up with advances in technology.

 

Digital Output

CD players have built-in digital-to-analog converters (DACs) so they can deliver a standard audio signal to the input of your receiver (or amplifier). If your CD player has a digital output, and your receiver is equipped with a digital input, you can bypass your CD player's D/A converter and send the digital signal directly to your receiver or recording unit.

The two most common types of digital outputs are coaxial and optical. Although coaxial connections usually have standard RCA-type connectors, the cable itself is specially designed to handle the much wider frequency bandwidth of digital signals.

With optical (Toslink) connections, the signal is transmitted as pulses of light through a cable housing a slender bundle of glass or plastic fibers. Optical transmission offers extremely wide bandwidth, ultra-low signal loss, and immunity to RF (radio frequency) interference.

In principle you can make perfect copies of digital material by making an exact copy of the digital code. In practice, errors will creep in and true perfection will not be achieved, but these errors are not likely to affect the sound. A digital copy will be far superior to an analogue copy in quality of sound and lack of background noise.

MiniDisc (MD) is a special case. In order to squeeze more music onto a smaller disc, some of the digital information is thrown away. The designers of the system use very clever techniques to make sure that only unimportant information is lost, and the latest MD machines sound very good indeed. However, MiniDisc is not, strictly speaking, a perfect copy.

For accurate copying, you would need a professional format such as Digital Audio Tape (DAT) which offers performance very slightly better than cd. CD-R (that is, recordable cd) can also offer recordings of cd quality. If you want to copy one of the higher-resolution, higher-bandwidth formats such as HDCD^® or DVD, then your recorder will need to have at least the same, and preferably higher, resolution and bandwidth. At present, only very high-end professional equipment can offer this facility.

 

 

Inside a modern CD player.  (Type Unkown)

 

Mega Changers

Some of the most popular CD players on the market at the moment are those that have a 5- or 6-disc playback tray. These are great for setting and forgetting the player, for having music on all day, or all night for a party. You can also store your discs and play them back in the same machine with 50-, 100-, or 200-CD disc libraries. These allow you to access your music without looking through the CD rack or fumbling through piles of covers. For complete audio automation, CD libraries can be daisy-chained together to hold your entire collection, even as it expands.  This not only increases your disc capacity, but in many cases also provides sophisticated playback options like cross-fading and no-delay shuffle play.  And for the ultimate, there's a high-end DVD and CD player/library that can tell you what's on any disc in your collection, and show you the cover via its online software connection. 

With a 60- to 400-disc "jukebox"-style changer, you can even store your CDs right in the player. Think of how much faster and easier it'll be to get straight to the music ... your entire CD collection will already be loaded and ready to go! (And think of all the space you'll save in your listening room once you've put all those plastic jewel boxes away in the closet.)  Mega changers make it easy to locate and program your personal listening selections. Some models with "Permanent Memory" even let you categorize your CDs by type of music (rock, jazz, classical, country) or artist (all Grateful Dead, Rolling Stones, etc.), or group each family member's personal favorites.  Never touch the disc again - just hit the remote

 

The Future of CD

Other types of CDs have also been introduced, requiring specialized players. CD-ROM (compact disc read-only memory) stores data primarily for readout through a computer, and other formats allow one to record and erase information on a disc. The DVD format is the successor to the CD and is already widely used to store feature films with multichannel sound tracks. Both DVD and CD have the same basic optical storage technology, but DVD offers dramatically increased storage capacity.

The next generation of CD-ROMs are called "DVD-ROM," and contains up to 4.7GB of storage on a single layer and on a single side. The capacity can be increased to more than 17GB by making the discs double sided and double-layered, which means the laser now reads through two substrate levels, and thus the CD contains double the information in the same vertical space. This is the new standard called DVD, agreed upon by CD manufacturers. DVDs will be able to store entire full-length movies on the space of a regularly-sized disc. Beyond that, double-layered, double-sided discs are waiting on the horizon, which will be able to store 26 times the amount of data of a conventional CD-ROM disc -- up to 17GB.

 

Super sounds of the future . . . here today with SACD!
Incredible as CD sound quality is, cutting-edge technology has made further improvement possible. Sony and Philips, co-developers of the original CD technology, have again teamed up to provide the next great leap forward in digital audio — Super Audio Compact Disc, or SACD.

The SACD format takes advantage of an entirely new recording technology called Direct Stream Digital (DSD). Standard CDs use 44.1kHz/16-bit PCM (44,100 samples-per-second Pulse Code Modulation, encoded at 16-bit resolution) to represent audio in digital form. DSD, on the other hand, is a 1-bit technology that samples music 2.82 million times per second, capturing 4 times more information. The resulting sound is warmer, smoother, and more "analog" than anything standard CDs can deliver.

DSD's exceptional dynamic range and ultra-high frequency response also enable the SACD format to faithfully reproduce high harmonics and room interactions present when the music was recorded. Bypassing several layers of filtration imposed by standard CD technology, SACD faithfully captures the music's purity and freshness, right down to the ambience of the studio or concert venue where it was performed.

Despite this advance over standard CD sound, SACD players don't turn their back on the predecessor technology — they're built to play either SACDs or CDs with glorious precision.

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Features of Compact Disc Digital Output   If you're only using the CD player to playback discs then you need not worry about a digital-output.   However if you are wanting to use your cd player with a Minidisc or CD-Recorder the you will need a digital-output. You can also upgrade your CD player by connecting an external DAC (Digital-Analogue-Converter)  to one of the outputs. Digital outputs are commonly available in two types;  Optical, also known as TOS-link and Coaxial (electrical).  The electrical type is sonically slightly superior.   Dimmable /  Display Off   One some players you can dim or turn off the display.   The display can often be a source of interference on a CD player and sonic benefits can be had with turning it of.  The NAIM players are equipped to do this and they flash the track numbers as they change.   Variable Output   Some players are equipped with a variable output.   This can be useful as it will allow you to bypass a pre-amp and plug straight into a power amp, giving significant sonic gains.   Remote Control   A feature that is found on most players.  Once you've lived with remote control, it's nigh on impossible to revert back.  Soon you won't even want to get out of your chair to change the disc.  In many single-brand systems you will receive a remote that controls both CD player and Amplifier   Auto Changer   The majority of CD players on the market are designed to play one disc at a time.  There are however, manufacturers who produce machines which offer CD multiplay machines that can take anywhere from three to three hundred discs.   The more sophisticated multiplay machines have features that allow you to assign certain discs to groups.  So all dance albums can be assigned to one group and jazz/blues to another.   Great for hours of uninterrupted music at parties These machines are great for convenience but that comes at a price.  A single disc player at the same price will outperform a multiplayer.  And often the multiplayer will be lacking that all important vital spark.   Playback facilities Search / Skip  This is the ability to select a specific track or skip various tracks.    Shuffle / Random  The ability to mix the tracks into a random sequence for playback    Repeat  The ability to play the same track over and over again    Program  The ability to program the track into any sequence the user requires.  Time Edit  When recording, this feature allows the user to program the CD player with the length of one side of a cassette.  The CD player then compiles the tracks in an order that best suits the tape length. Fade Edit   When recording from the CD, the signal is faded at the end to provide seamless recordings. Music Calendar  A visual indicator of the number of tracks on the disc and which track is currently playing. CD Text   Is a system which allows suitable players to display basic information such as track name, album title and artist name.   The system only works with suitably encoded discs such as Titanic OST for example. HDCD   High Definition Compatible Digital is a coding system for CD which all for more data to be stored on a disc and as such better sound.   To get the full effect from an HDCD you will need a player that is equipped with an HDCD decoder.   The PMD100 is a common decoder for HDCD.  Incidentally the format was launched by Pacific Microsonics of California.

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Mick Evans 1999-2001

  [email protected]

[email protected]