AV Cables Basics
Guide to Audio Cables and Connectors
Discussing both analog and digital audio interconnects
The advent of HDMI — with its ability to carry both video and audio—has somewhat simplified home theater connectivity. Yet, at the audio level we still encounter various types of cables carrying analog and digital audio between the different system components in a home entertainment setup.
In this short audio cable guide, we discuss the most common type of audio interconnects found in the home theater.
Audio Interconnect Basics
Typical analog audio cables consist of RCA or BNC connectors terminated over a coaxial cable.
Cables for multi-channel audio are characterized by a separate cable connection, one for each channel; color coding is normally used to facility identification between the different channels in the audio setup.
Digital audio cables may use either a single coaxial connection or a single optical connection; the latter is known as TOSLINK and makes use of a fiber optic cable to transfer audio signals via pulses of red light from a digital source.
Good quality cables use precision engineering technology and pure copper conductors often in the form of oxygen-free copper (OFC) to ensure that audio signals pass with minimal loss and remain unaffected by both electro-magnetic and radio frequency interference. Exotic cables may also use thick silver coating of the copper conductors to improve connectivity; but the real primary benefit of silver coated conductors is that this silver coating helps to improve the connection between the conductor and end connectors.
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Most high quality cables also include two separate shields—a braided copper shield to guard against RFI, and one made of foil to guard against EMI. In some cables, the shield is grounded only on the end that connects to the source so that interference will drain away from the destination end of the cable.
These cables incorporate directional arrows printed on the outer jackets and should be hooked up with the arrow pointing away from the source (i.e. the arrow should be pointing in the same direction as the signal flow from source to load).
Connectors are extremely important to the overall cable quality. Good RCA and BNC coaxial connectors provide constant, high-pressure contact with the respective systems terminations. The use of gold plated connectors in high quality audio cables is your guarantee for a corrosion-free connection. This is necessary to ensure continued high quality signal transfer between system components—one that would not degrade over time.
End Connectors used in Audio Applications
RCA Audio Terminated Cables
These represent the most common connectors in use for audio applications. Used on both analog inputs and outputs, these connectors come in color-coded pairs, usually red for right and black (or white) for left. These represent inexpensive audio cable options for Audio CD, DVD-Audio, and stereo playback in general.
RCA-terminated adaptor cables are also available; these come with one end of the audio cable terminated with an RCA connector and the other with a different audio connector. The Mediabridge stereo audio cable shown here and available from amazon serves as an adaptor cable between 3.5mm jack and RCA; this makes it suitable for use as an audio interconnect between say an MP3 or Smartphone and an AV receiver.
BNC is a secure bayonet-style locking connector that is found on both audio and video cables. It is mainly used on professional video gear and high-end consumer audio and video systems.
IRCA to RCA and BNC to either RCA or BNC coaxial cables can be used in both analog and digital audio applications. 'Coaxial' is that type of cable where the signal carrier (inner conductor) and its shield are aligned along the same axis (generally a signal wire runs down the middle of a cylindrical shield).
The fact that these same connectors are used on both coaxial audio and video cables does not imply that it is possible to interchange video with audio cables. Irrespective of the similarities in physical appearance, cables designed for video applications have to support a wider frequency response than that required for audio systems.
Optical Digital Audio Interconnects
Optical audio cables are a special subset of audio interconnects that make use of pulses of light to transmit signal information between system components over an optical fiber connection.
Monster ILS100-1M LightSpeed High Performance Toslink Fiber Optic Audio Cable (1 meter)
The most common type of optical connector found on home theater cables is the Toslink connector shown here.
Originally developed by Toshiba (hence Tos link), this connector is usually made from plastic. Some portable players make use of the mini-optical jack—an optical connector similar in appearance to the standard audio mini jack plug.
The main advantage of a digital interconnect is that these are not susceptible to electromagnetic and radio frequency interference.
Due to light attenuation within the optical fiber, Toslink interconnects are limited to a maximum length of 33ft/10m.
Theoretically, these can come relatively cheap in comparison to regular metal interconnects, however, keep in mind that there is always a price to pay for a quality interconnect especially when high tech engineering is involved.
Premium Toslink connectors make use of graded index optical fiber to reduce jitter for enhanced definition, spring loaded connectors to keep the fiber in correct optical alignment for maximum data transfer, and a metal-shell connector for long life durability.
Toslink optical fiber connection systems support all modern audio formats, including Dolby Digital Plus, TrueHD and DTS HD. It is found on DVD and Blu-ray players, CDs, game consoles, etc.