Digital Cables
Digital cables are used to transfer digital data from one component to another. This page introduces you to how digital cables are used for home recording, for improving sound quality of compact disc, and for getting digital surround sound from DVD.



Digitally recorded soundtracks on DVD, CD, etc. are encoded onto the discs as a stream of information. The information is only turned into sound when it passes through a Digital-to-Analogue Converter, or DAC, where it is converted into an analogue wave form that can be fed to an amplifier. Until the data stream reaches the DAC, the soundtrack is nothing more than digital information. In this pure, unprocessed form, the data can be transported between components within a hi-fior home cinema system with almost no loss of quality, whereas an analogue signal is degraded slightly each time it passes out of one unit and into another. It is therefore better to send the digital stream between components as digital information before it reaches a DAC in order to get the best final sound. Digital connections allow you to do this, and come in two types - Optical (using a fibre-optic cable to carry the data as flashes of light) and Coaxial (carrying an electrical signal along coaxial cable). Components that can use digital cables to transfer information will have one, or both, of these type of connections. Just make sure that both boxes you are connecting together have at least one that is the same!

You may have seen Video Sources like DVD players, Laserdisc players and CD players with a digital output on the back. Other components have digital inputs to receive the digital signal. This raw digital signal can be used in a number of ways to make the most of the equipment you are using.

Optichord ProDAC
Digital cables by the Chord Company. On the left is the Optichord optical cable, and on the right is the ProDAC coaxial cable.


CD players sometimes have a digital output on the back. This is used for sending the digital audio information from the player to an external Digital-to-Analogue Converter, known as a DAC. All CD players have two main sections - the Transport (which holds the disc and reads the information) and a DAC (for converting the digital information to an analogue signal). Both these sections are normally contained within the same casing. When an external DAC is added to a CD player, the player becomes a CD Transport only, with the information processing taking place within the DAC. The advantage of this two-box system is that the external DAC can offer an improved sound quality by processing the digital information faster or in a different way. A two-box system will also reduce the amount of internal interference caused by the close proximity of the internal circuits in a single-box player.

An external DAC will have a digital input for receiving the digital data stream from the source, and a pair of phono stereo outputs for sending the decoded analogue signal to an Amplifier. CD Players can also be connected to a Minidisc recording deck or a CD-R deck using a digital cable to increase the quality of a CD sourced recording.

The diagram below shown how an External Digital-To-Analogue Converter (DAC) is connected to a suitable CD Player and Amplifier:  


External DAC Diagram



All DVD Players have digital outputs that can be used in a number of ways depending on the type of player you use. As with a CD Player, an external DAC can be added to improve the sound. However, the DAC found within the majority of DVD Players is commonly superior to external DAC's in terms of processing speed and data capacity, so adding one to DVD Player is unlikely to produce improvements as obvious as with a CD player.

The main reason for including digital outputs on a DVD Player is for connecting the player to a separate digital surround sound decoder. To hear digital surround, such as Dolby Digital 5.1, the data from the disc must be sent to the decoder using digital cable. A DVD player without a built-in Dolby Digital decoder needs to be connected to an home cinema amplifier or separate decoder using a digital cable. A DVD player that has its own internal Dolby Digital decoder is connected to a home cinema amplifier or processor using a six-channel phono connection, one for each of the decoded 5.1 audio channels.

You can also use the digital connection to send audio signals to a digital recording deck, such as Minidisc or CD-R. Some DVD players can also output a stereo soundtrack as a digital signal known a Linear PCM and allows the addition of an external DAC for stereo audio playback The PCM signal can also be used to improve sound quality of stereo CD playback when a DVD player is connected to an amplifier using a digital cable.

Connections for digital surround sound in home cinema systems are explained in more detail in the DVD Digital Connections area.


Minidisc and CD Recording decks

Digital recorders also benefit from digital connections. A CD or DVD Player can be connected to a Minidisc recorder using a digital cable to achieve a high quality audio copy almost identical to the original. There is very little data loss through a digital cable when compared to the traditional analogue phono interconnects. (Note: only CD's can be copied from a DVD player - DVD's are copy protected)