What to Look For In Cables
- Type of Signal / Interconnect
- Signal and Interconnect Compatibility
- Analog vs. Digital
- Build Quality
- Length of Cable
- Surrounding Environment
- Twisted or Untwisted Conductors
1. Type of Signal / Interconnect
Know the limitations of the signal/interconnect your cable will use. For example, a RCA analog interconnect can not carry 5.1 surround sound audio over a single cable. Another example is that a S-video interconnect can not carry high definition video. See the video, audio, and data interconnect sections for more information on the capabilities and limitations of each signal/interconnect.
2. Signal and Interconnect Compatibility
A cable’s interconnect and the type of signals they carry are typically tied together to help stop confusion. However, this is not always the case. For example, a VGA 15 pin D-sub will normally carry a RGB video signal, but in rare cases, it can carry YPbPr component signals. Some, but not all DVI interconnects can carry analog RGB video along with digital video. Problems with signal/interconnect compatibility is more prevalent in video, than audio or data. Make sure you understand your video, audio, and data interconnects and what type of signals they can transmit before purchasing any cables.
3. Analog vs. Digital
There has always been debates on whether high quality cables (and more expensive!) will transmit higher quality video/audio than its cheaper counterparts. About 75% of the answer to this question is dependent on whether the signal is analog or digital.
As an analog or digital signal travels down a cable, it is constantly bombarded by electromagnetic waves. ElectoMagnetic Interference (EMI) comes from many sources including over-the-air television, radio, and cell phone signals, as well as the wiring in your house. Unless a cable has proper shielding, EMI waves hitting a cable can generate a small current to produce noise on the signal.
The diagram above shows how noise will affect analog signals far more than digital signals. This is because digital signals are either on or off. In low voltage signals, this usually means 5 Volts (on) or 0 Volts (off). There is no affect by the small change in voltage from EMI. For example, EMI noise can reduce 5 Volts to 4.6 Volts. A digital device will take the 4.6 Volts and interpret it as its original 5 Volts. On the other hand, an analog signal would not do any conversion, and would incorrectly read the voltage as 4.6 Volts.
Make sure your cables that carry high-frequency analog signals are properly shielded to block out any EMI noise. Cables that carry digital signals should still be shielded, but high quality shielding is not as important as in analog signal cables (for cable lengths under 10 feet only).