Chances are that when you are putting together your new PC battle station or home theater. The last thing one your mind is cable length. You only want to make sure that you can get from point A to B. Other than that how much does it really matter in an age when most things are digital and the usual mantra of IT experts, when it comes to cables is, it either works or it does not. We just coil up the excess and throw it in a corner. Let's start by discussing things that are still analog, cables of speaker, wires, VGA cables you might still be using for older monitors and RCA cables for connecting audio video equipment that does not have digital Jack such as HDMI or TOSLINK.
Analog signals depend on small continuous changes in an electrical wave form. Analog signals rely on precise variations in voltage they are susceptible to interference as well as degradation. The longer they have to travel, the worst this gets. This is the reason shorter cables are better as well as thicker ones since they have a less electrical impedance which keeps your signal from traveling as far as it needs to . This results in an actual improvement in picture or audio quality. But if you are gone completely digital you might be a little surprised to know that length can still matter for reasons other than not wanting to have a huge tangled mess of wires behind your setup.
Let's begin with HDMI the common perception about HDMI cables is that the expensive cables are better than others.
However that is not the case, almost all of them are of the same quality. Length is irrelevant in the context of digital signals. Digital signals are much less susceptible to interference because information is being sent in discrete binary chunks rather than a continuous wave form so over short distances. This means that the if the signal works it works, and no fancy expensive cable or shorter cable will make your colors brighter or your sounds clearer. But there is a limit too. HDMI cables that are longer than 50 feet or 15 meters can result signal drops unless you use a repeater or an active cable with built-in electronics that boost the signal but it is not just audio video cables that had issues with signal strength. USB cables have a maximum recommended length of five meters for USB 2. For USB 3.0 it reduces to 3 meters. USB 3.1 10-gigabit has 1 meter recommended cable length. That is due to electrical reflections that can happen if there is not enough of a delay between each bit of information being sent down the cable. So it is this delay that limits how long the cable can be while still transmitting data effectively but again the solution is pretty simple and an active cable or a powered USB hub that acts as a repeater can bridge the gap. So if you like you can even connect a pair of USB with an Ethernet cable since both cat 5 and cat 6 cables can reach a hundred meters before signal losses and interference with other circuits, called cross-talk, start to become a problem.
So far we have only talked about traditional copper cabling what if you are using an optical cable instead something like TOSLINK for surround sound or an optical thunder bolt cable. Optical cables use light which can be attenuated if the cable is not constructed well meaning that it loses intensity at range along with its ability to carry information think about how flashlight or the headlamp on your car visibly get less powerful the further away you are this is a common problem in TOSLINK cables which tend to be constructed with cheap plastic fiber limiting their range to 10 meters at the most on the other hand the more premium Thunderbolt cable are often made of data grade glass fibers which can reflect a light beam down the pipe with far less attenuation meaning you can get them in length up to 60 meters at least for Thunderbolt 2.
So keep these tips in mind if you find yourself needing a long cable run. It is one of those few times in life where longer does not necessarily mean better