Throughout the history of audio technology, numerous interconnecting cables have been used in an attempt to find the most practical balance between sound quality, durability and cost. As a result there are a variety of different termination connectors that can be fitted to the ends of audio cables.
TRS Analog Connectors
These are one of the longest-serving styles of audio connectors; you have probably seen one of the varieties used in common home audio applications. The largest size is 6.35 millimeters and is commonly used for guitar cables and karaoke microphones. The smaller varieties generally come in 2.5 or 3.5 millimeters and are used as headphone connectors for cellphones and personal audio players. The cylindrical body of the connector is broken up by plastic bands and each sector handles part of the signal. A stereo connector will have two bands, dividing the connector into left, right and ground signals.
RCA or Phono Analog Connectors
Named for the RCA record company who first introduced this connector for their home phonographs, these connectors are commonly seen as interconnects on home audio equipment. They are usually sold as a pair of cables, bonded together, with white and red color-coded connectors for the left and right sockets. This connector type is also used for Standard definition S-Video connections from cameras and camcorders.
XLR Balanced Connectors
XLR stands for "External Live Return." These three-pin connectors are primarily used in professional audio applications such as studio condenser microphones and public address mixers. However, they do appear on some high-end home audio equipment like Cyrus amplifiers. XLR cables and connectors are voltage-balanced to resist noise. In addition to the two signal-carrying wires connected to the first two pins, a third carries the signal from the cable's shield. This allows the variations in voltage to be subtracted from the final audio signal for low-noise performance.
Digital Optical Connectors
Sometimes referred to as SPDIF or TOSlink, these connectors use a fiber optic cable to transmit digital signals as light. They include a pair of lenses mounted to locking connectors at either end of a flexible length of glass-fiber cable. They're used for a variety of applications; audio interconnects, speaker cables and as the outputs from PC sound-cards. One of their few drawbacks is that it a complex technical process to produce custom cables by fitting your own connectors to a length of fiber.
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