Why CDs?
Why CDs?
Clarity Defined
CD players nowadays are everywhere. This is because CDs offer unparalleled sound which is extremely convenient to store and to play. You could for example, put half a dozen CD discs into your pocket and not know they were there... try doing that with six vinyl records! Although there is still much debate about sound quality from certain quarters, it is certainly the most widely-used and easily-obtained music source available on the planet today.
When it was introduced in 1983 no one knew how much of an impact it would have on the world in just twenty short years. It would be safe to assume that most households in the Western world has at least one CD player - try buying your music on any other format and you'll soon encounter problems! However, according to some audio experts, the sound differences among the cheaper end of CD players are very small, even to critical listeners. It's often other components of a hi-fi system which show up the limitations of CDs.
That's why when choosing a CD player, a user's main concerns should be ease of use and playback features (as well as blending it in to the rest of a hi-fi system).
A Short History of the Compact Disc
In the early 1970s, Sony, Philips and a number of other electronics companies began to plan for a commercially viable medium for digital audio. The standard sample rate of 44.1 kilobits per second (Kbps) was a compromise dictated by conflicting desires for maximum playing time, highest fidelity, fabrication ability and overall costs. At this early stage of its development though, like the early compact cassettes system, there was no concept of home recording and no prospect of the technology we use today on a routine basis.
44.1 Kbps was the highest sampling rate possible in mass-producible silicon in the late 70s and early 80s when the standard was set. In fact, 16 bits of resolution turned out to be rather more difficult than was expected — the first Philips players had oversampled 14 bit D/A converters. When talking of the maximum playing time of a CD, a popular misconception of the time said that Akio Morita, the founder and chairman of Sony, specified a 74-minute playing time so that Beethoven's Ninth Symphony could be played without interruption. However, according to Kees Schouhammer-Immink, Philips' top scientist on the team of Sony and Philips engineers which designed the CD, that story is revisionist fiction. The diameter of the CD was originally specified to be the diagonal dimension of the compact cassette and was then rounded to an even number. Given the sampling rate, bit depth, error correction and practical optical density at the time, the result was a playing time of 74 minutes.
So what are the options?
The vast majority of CD players are single-disc players. Players such as BeoSounds Century, Ouverture or 3000 allow only one CD to be played at a time. However, with Bang & Olufsen's BeoSound 9000 six CDs may be placed within it to provide over seven hours of music. Some CD changers allow users to load from 5 to 300 CDs and play them in any order. CD changers come in several different types - cartridge, carousel and 'jukebox':
Cartridge changers allow you to load six CDs into a cartridge and then slip the cartridge into the player. A loaded cartridge can play six hours or more of continuous music. Additional cartridges can be purchased, allowing you to prepare multiple groups of CDs for immediate play.
Carousel models are the best-selling variety of CD changer. They are similar in construction to a single-disc player; a retractable tray can be loaded with five or six CDs at a time. Many models allow you to load and remove discs while one CD is still playing.
Jukebox players are of the type that you might see in your local public house - they hold a large number (usually over 200 CDs) from which a user can choose.
How much do they cost?
A good-sounding, reliable CD player with no remote control can be purchased for much less than 150 euros. Single-disc models with remote control and carousel changers, start at about 150 euros. Cartridge and jukebox models can be considerably more expensive though.
What are the main choice criteria?
If you're on a budget and you don't mind changing a CD every 45 minutes or so, a single-disc player might be for you. But if you can afford to move up to a CD changer, you'll greatly increase your listening options.
Cartridge models hold multiple CDs. But reloading a cartridge - or choosing a single CD from your collection and playing it - can be a hassle, because you have to load it into the cartridge first and then plug the cartridge into the deck.
If you want to spend the least amount of time handling your CDs, you might want to choose a Jukebox model. Unless you have a really large collection, you can store all of your CDs in the changer. You can program your CDs to play in any order or flip through and find the titles and tracks you want to hear and display them on the readout. On some players, before you can do this you'll have to enter the titles and tracks into the changer's memory.
Carousel players don't offer the huge capacity of jukebox changers, but they provide a nice combination of storage, accessibility and ease of use. You can store up to six CDs in a carousel changer and program hours of your favourite music. The retractable tray makes it easy to access and change CDs during play.
If holding and playing a large number of CDs is essential to you, then perhaps Bang & Olufsen's BeoPlayer would be a better way of storing and playing your favourite tracks. With this system, once CD tracks have been converted to a suitable computer format, they can be played back around the house. Another new innovation is the using of hard drives to store and play back your music collection by way of a computer-type hard drive.
What is Super Audio?
Two new DVD-based audio formats have recently been released onto the market: DVD Audio and Super Audio CD. Super Audio CD, despite its name, is actually a DVD format. Like DVD movies, they will both offer the potential for six-channel surround sound (see Why DVD ?).
Super Audio CDs will offer sound quality that is audibly better than current audio CDs - especially when played on a high-performance system. Some of the first Super Audio discs will play on today's CD players - but only in two-channel sound. Some more expensive Super Audio players will be able to play Super Audio CDs in full, six-channel sound. However, Super Audio CDs are likely to cost quite a lot as compared to CD-R disks which cost less nowadays than a floppy disk!
In 2002 only Super Audio's creators, Philips Electronics and Sony, along with a handful of independent specialty record labels, have committed to manufacturing Super Audio discs. No major record labels or retailers have yet committed to selling them.
DVD Audio discs, like Super Audio CDs, will offer six-channel sound that is much better than that of current CDs. The new discs can't be played on CD players - or even on current DVD players. Audio DVD players and combo-DVD players - which play both DVD movie and DVD music discs - will be available soon. DVD Audio discs, which will be produced by all major music publishers and carried at most major audio retailers, are expected to run at a premium price as compared to their CD counterparts. DVD audio players too are likely to cost much more at first. However, as the format war is eventually won by a major player and both hardware and software is mass produced, then prices are likely to tumble.
What other features should I look for?
Although the most important feature of a CD player is probably the number of discs it holds and stores, here are few more features to consider when contemplating a CD player purchase:
Remote control
- a remote control adds convenience to your CD player. Some receivers have remotes that will control CD players from the same manufacturerDirect track access
- with direct track access you can go directly to any track on a CD at the touch of a buttonProgramming
- programming capabilities vary from the simple to the complex. You can do something as simple as playing songs in any order or as complex as skipping all the songs you don't like on your entire 200-disc collection. Before you buy, be sure of the programming capabilities of the model you've chosenDigital output
- some CD players allow for the perfect digital transfer of audio information. With digital output, you can use your CD player as a source of audio signals for your Minidisk recorder, Digital Audio Tape deck or external digital-to-analogue converterPrinciples of digital audio
Sampling:
Given an analogue audio signal, a process is needed to bring it into the digital domain. This process is sampling and it is dictated by the Nyquist sampling theorem which states how quickly samples must be taken to ensure an accurate representation of the analogue signal.
The sampling theorem is quite simple. It states that the sampling frequency must be greater than or equal to the highest frequency in the original analogue signal.
To use sampling in a digital audio system, two constraints must be observed. The first is that the original signal must be band-limited to half the sampling frequency by being passed through an ideal low-pass filter; the second is that the output signal must again be passed through an ideal low-pass filter to reproduce the analogue signal. These constraints are crucial to sampling and if not observed will lead to an unwanted effect known as aliasing.
Aliasing:
Aliasing is a system's erroneous response that manifests itself when the constraints of the sampling theorem are not observed. Aliasing will surface in the audio signal as audible distortion. For the limiting case of a frequency at exactly half the sampling frequency, there will be only two samples generated - this is the minimum required to represent any waveform.
Created: 10th January 2007
Modified: 2nd April 2007
