Audio: Wires and Connectors

WIRES AND CONNECTORS

Wires and connectors link audio components together to form an audio system. Although there are quite a number of different standard connectors and cables, they all carry more or less a variation of the same type of audio signal: a voltage fluctuation corresponding to sound waveforms. The only major differences arise when comparing analogue sound to digital sound.

Shielding

Audio voltages are sometimes measured in millivolts and fractions of a volt. At such low voltages, it is highly susceptible to interference from outside sources. Such interference is sometimes created by the existence of electromagnetic radiation around the audio cable. EM radiation can result from any nearby electrical components, cables, or even neighbouring radio stations. Components that utilize large amounts of energy, fluorescent and halogen lights and those that have motors or transformers are usually the worst culprits. The current in the circuits of these components create a fluctuation electromagnetic field around the component. This field in turn induces undesirable currents in neighbouring circuits. If the neighbouring circuits are audio cables, the result can sometimes be audible as hum, noise or occasionally distortion.

In order to avoid interference, insulated audio cables are usually surrounded by a layer of shielding. This is a flexible metal cylinder of wire or foil that surrounds the actual audio cable. The whole bundle of shielding and insulated audio cable is usually surrounded by another layer of insulation.

The theory is that the metal layer formed by the shielding will absorb most of the influence of EM fields, reducing the impact of EM radiation on the signal cable inside. The resulting audio signal would be freer from the noise and hum of EM fields. This theory works reasonably well for areas of low EM radiation.

Some cables are arranged such that there is one signal conductor in the centre surrounded by a cylinder of shielding. These are sometimes termed co-axial cables, because the cross-section of both wires have the same circular centre (axis). This means that the signal cable is about the same distance away from the shielding at any point in the cable. This is desirable because that means that the shielding capability of the cable is uniform across the whole cable. It also means that if the shielding does carry a current of its own, the EM fields generated by the current should automatically cancel out when it reaches the signal cable, and vice-versa.

Cables with one signal conductor and one shielding layer are called unbalanced. The exception is with stereo cables, in which two signal carrying cables may share one shielding. Although they have two signal conductors, they are also carrying two separate signals, so they are in effect two unbalanced cables in one.

Shielding and weight

Shielding is usually found as either a foil sheath under the top layer of insulation of a cable, a twisted coil of wire around the inner cable, or certain expensive cables use a conductive plastic/graphite insulator as shielding. Professional mic cables usually employ a braided sheath of copper wire, as this is not easily unravelled and lends strength and rigidity to the cable. Foil is a good shielding for cables that do not see much rough use, as it is thin and light. It is especially appropriate in a studio situation, where a patchbay can have 40 or more cables running into it. If braided heavy mic cable was used, the shielding would probably be very effective but the weight of over 40 cables would probably pull the patchbay off the rack.

Balancing

Shielding has its limitations. Strong EM fields can still affect the inner signal cable to an audible degree. As such, a second method of preventing interference, known as balancing, is used in professional applications and low-voltage equipment (microphones, for example). This uses two cables to carry one signal and usually one layer of shield.
One cable is known as 'Hot', the second is known as 'Cold', and the shielding is known as 'Shield' or 'Ground'. The 'Hot' and 'Cold' is usually used for unbalanced signals, in which one cable carries the signal and the other serves as a return path of the signal. However, since the convention stands, the naming is the same for the balanced cables. In balanced cables, both serve as signal carries for inverted signals.

The shielding in balanced cables acts as normal, but the two insulated cables are twisted together and kept as close together as possible. The theory is that, as the two cables are kept as close as possible to each other while still being insulated from each other, any EM radiation that penetrates the shield will affect both cables equally.

In order to remove the artifacts produced by the interference, one of the signals can be reversed, and mixed with the other signal. According to high-school physics, if the artifacts on both cables are identical, the reversal and mixing of the signals will cancel out the noise.

Of course, if the signals between the two signal cables are also identical, the reversal and mixing of the signals would also result in a cancellation of the signal, which means you won't get any sound at all. Duh. Therefore, before the signal is introduced into the cable, one is already reversed. When the reversal occurs again at the receiving end of the cable, the signal strength would be doubled, and the noise should be cancelled.

This method of noise cancellation works rather well, especially if the source of the EM fields are some distance away from the cables. If the field source is too close, or if the area surrounding the cable has varying EM absorption and reflection properties, then the EM field imposed on the two signal cables may not be identical, and the noise cancellation would be less effective.

Ground Loops

According to electrical physics, a loop of wire placed in an area with a fluctuating EM field could quite possibly have a current induced in it. In audio terms, your cables could quite possibly be generating current due to the EM fields in the vicinity. A loop in the cables would allow the noise or hum to increase in power quite considerably, resulting in noise or an audible. But in most installations, signals are not looped. Doing so would result in feedback, the high pitched wail that you hear when you stick a microphone near its own speaker.

Grounding and shielding in the cables, though, are another matter. Equipment that require large amounts of power will probably be grounded, especially if your mains voltages are 220V instead of the American 110V standard. This will reduce the possibility of a fatal shock should your equipment short circuit for any reason. Everything is connected to a single mains earth, which is usually connected to all the earth pins in all the power sockets in one room.

This would normally be okay, as the grounding is only connected to each other in a star-like fashion. From a central earth wire (leading to the real Earth via a grounding cable or metal pipe) earth cables run through your power cables into the equipment. Once you take into account that some of your equipment is linked with shielded cables, the equation gets more difficult.

Currents could quite possibly run from one piece of equipment, into the earth cable, into another piece of equipment, then back to the first piece via a shielded audio cable. The result is similar to feedback: the unwanted signal from the current will be amplified until it is audible and clearly undesireable.

Getting rid of ground loops are not easy. Finding them is even harder. The only acceptable method is to remove and disconnect everything, and reinstall the equipment piece by piece. Stop when the hum becomes audible, and fix the problem in the last piece of equipment that was installed. It is possible to solve the problem by systematically unplugging and replugging cables until the change in one particular cable results in a dramatic change in hum, and fix it there, but this is purely a short-term solution. Any further change to the set-up may result in the loop reappearing.

To kill a ground loop, the common-sense method would be to break the loop. Removing the earth cables from the equipment to the mains is not recommended, but it works. You just have to be careful not to electrocute yourself.

Breaking the shielding of a cable is possible, but it renders the cable susceptible to the influences of EM fields. However, breaking a cable is effectively introducing an infinite resistance into the shield. How about introducing just a little resistance into the shield?

This actually works to some degree. Some connectors might be able to accomodate a small resistor into the casing. The shield of the cable would thus be soldered to the resistor, and the resistor soldered into the shield contact on the connector. A resistor of about 100ohms would be sufficient. What it actually does is reduce the current produced by a ground loop to a level where it is hopefully inaudible, even though it still exists.

If the effects of EM fields become audible, it might also work to introduce a 4 pF capacitor parallel to the resistor (where you have space for this, I have no idea). This would even out the currents so that instead of fluctuating and becoming audible, they would remain at a similar level continuously.

Actually, a well designed piece of equipment will have a ground lift. This is a 100ohm or so resistor between the mains ground of the equipment and all the shielding contacts of a piece of equipment. This would reduce possibilities of audible ground loops. A truly covers-all bases piece of equipment would have a switch to activate or deactivate the ground lift. In real life, some DI boxes have this facility, in their quest to match levels and reduce interference. To test if your equipment has ground lift, insert a balanced TRS or XLR cable into the equipment, and measure the resistance between the shield contact of the exposed connector and the casing of the equipment or the earth pin of the mains cable of the equipment, using a multimeter. If there's a 100ohm to 500ohm resistance, your equipment is ground lifted.

Speaker Cables

Speakers require far more power than microphone or line-level inputs. As such, they require cables with a thicker guage of metal wire, if not, they might overheat and burn up. Also, since the signal power is so large, noise is much less a problem, so shielding is not so common on speaker cables, although shielded speaker cables do exist (I know, I use them). Speaker cables come in all shapes and thicknesses, so it's hard to typify them. Generally, cables for microphones or guitars are thick and smooth, due to the shielding and the insulation. Cables of line signals can sometimes be thinner, due to lack of balancing or foil shielding, although balanced line signals can be carried in cables as thick as mic cables. Speaker cables are either flattish (for home installations, to avoid a messy looking cable), bumpy (due to lack of insulation and a thick wire guage) or even just a pair of black and red wires twisted together (the most flexible and easily replaceable, always potentially a tangle hazard).

Types of Cable

Cables used to transfer audio information are usually made of metal. Cheap cables could be the type of copper cables you might expect to find in lighting or mains wiring. Usually cheap cable could be pressed into service in a hurry, especially when using bare-wire connectors. This of course also implies that the cheapest cables are used for speaker connections. As above, ensure that speaker cables are capable of handling the high electrical power of speakers or they might melt.

More expensive types of metal cables, in order of cost, range from Oxygen-Free Copper (OFC), Silver and Gold. OFC is longer lasting than plain copper and allows less distortion to corrupt the audio signal passing through it. Silver cables and Gold cables are usually reserved for audiophile applications, and the improvement in sound is usually minimal for the casual listener.

There are non-metal cables for audio, typically not used for speaker connections. Graphite, the stuff that makes pencil 'lead' black and writeable, can actually conduct an electric current when it is passed in a certain orientation relative to its atomic structure. Graphite cables are available, but are very difficult, if not impossible to solder on your own. They have to be made at the factory. They are supposed to be less susceptible to incidental electromagnetic fields than metal cables, and do not bias the sound in any way. In effect, a very neutral, distortionless cable. Also very expensive.

Plastic polymer cables are also available, but I have not come across them yet. I'll update this page with relevant information when I get the chance.

Connectors

There are a number of different types of connectors used to affix cables to equipment. Balanced equipment requires at least three separate points of contact from the cable to the equipment, while unbalanced equipment requires at least two. Stereo unbalanced connectors requires at least three. Confused? Read on.

Jack or connector?

What is the difference between a jack or a connector? Although terminology varies from place to place, a jack is usually used to refer the outlet or inlet on equipment that allows a cable to be inserted and connector. A connector is found on the ends of a cable. A cable connector will plug into an appropriate equipment jack. Both jacks and cables can come in female and male versions.

XLR connectors

XLR connectors come in several names: Switchcraft, Cannon, and XLR. They are all basically the same. The difference is in the manufacturer of the connector and how the connector is built. All different forms of XLR can be readily connected with another XLR jack or connector.

XLRs have an interesting male-female convention. Whereas most other connectors just have female on the jacks and male on the connectors, XLR can have either on either side. Although this seems like an unnecessary hassle, it is actually an advantage of XLR. The rule of thumb is: if the jack/connector is to be connected to a source of audio signal, then it should be a female. If the jack/connector is to be connected to a receiver of an audio signal, then it is a male. This is an easily understood convention for anybody past puberty, so equipment with XLR connectors are usually wired up correctly (with occasional blunders). Cables typically would have male on one end and female on the other, thus making the extension of XLR cables really easy: just plug in another cable. No adaptors required.

XLR is also a very secure type of connector. A well-made XLR connector would have a metal cylinder with three pins inside. The pins are arranged in an isosceles triangle to avoid connecting the cable the wrong way round. The pins connect up the shield, the male and the female conductors, and are usually clearly numbered on the connector. The cylinder is not an electrical signal carrier at all, it is just a rigid protective covering. A clip at the top of the female cylinder fits into a rectangular gap on the male cylinder, making a secure and audible 'click' when the two parts are connected. The connectors/jacks cannot be removed once a connection is made unless the clip is depressed, or a very strong force is exerted on the cable, in which case, the cable will probably snap at the same time. A rubber or plastic tube forms a grip for the cable so that it is not easily broken off the connector.

As you might have deduced by the three pins, XLR is typically a connector for balanced cables. An XLR-to-unbalanced cable can be made by connecting the shield with the cold conductor at any point of the cable, but this would lose the signal strength and the noise cancellation abilities of the balanced connectors.

Unfortunately, there is a strange variation of the XLR standard that exists in some European standards. This mixes up the connectors such that the first pin is the hot conductor, the second pin is the cold conductor and the third pin is the shield.

Although there are pre-made XLR cables on the market, XLR jacks are usually sold separately for professionals to solder to cables of their choice of length and type. Cannon, Switchcraft and Neutrik are three well-known brands of XLR connectors. Cannons are the originals, but I haven't had much experience assembling these.

Switchcraft connectors are more durable, but when disassembled, separate into several small pieces. This could make assembly a little trickier. For example, the spring for the clip-button on the female connectors can fall out of the assembly when the connector is unscrewed. Lose anything and you'll have an imperfect connector. The durability of Switchcraft connectors is far superior to most other connectors. Miniature screws, the type only accessible to jeweller's screwdrivers, are used extensively in the assemblage.

Neutrik (of Switzerland) make the easiest to assemble XLR connectors. They come in about 4 easy-to-handle pieces. Grooves inside the parts help each piece slide in the correct direction and orientation. No screwdrivers are required for assembly. The metal casing seems a little thinner than Switchcraft's, but don't dent easily unless (like I have) thrown from two or more stories onto concrete. Note that a dented male connector is typically a useless connector, since it's almost impossible to un-dent it and the female connector will never fit with a damaged male connector.

Neutrik's connectors have cable grips that, although easy to assemble (just screw them in), don't seem as rock-solid as Switchcraft grips. Neutrik connectors may be a little less resistant to tension in cables, but I have had no problems with them in the past.

Addendum: I've recently received the following insightful mail. For the record, most gear I've seen uses pin 1 shield, pin 2 hot and pin 3 cold.

From: "David Hood" <mstbragg@fayettevillenc.com> To: <firehzrd@pacific.net.sg> Subject: XLR Connector standards Date: Tue, 15 Jun 1999 17:12:34 -0400 Hi there... I really appreciate the web site and the info. I was looking for information on connection standards for XLR connectors that I didn't have to buy and so far your site comes closest. I did see that you referred to the obscure European convention of wiring Pin 1 hot but you never comitted to what you thought the correct convention should be. This came up today because a manufacturer assured me that Pin 3 should be hot because the RIAA said so. We have been building systems for years with Pin 2 hot and have only run across one manufacturer that consistently wires Pin 3 hot, that one being Denon. So far I have checked the following organizations and am sticking with Pin 2 hot: National Association of Broadcasters - Engineering Handbook Edition 8 Pg 770 ANSI Standard S4.48-1992 (you have to buy this) EIA Standard 221-A (you have to buy this) AES Standard 14-1992 (r1998) (you have to buy this) SMPTE Reccomended Procedure 148-1987 (you have to buy this) EBU Technical Recommendation R50-1998 (free on line - this is the only one I actually obtained) Oddly enough, neither SBE or NARTE had anything about standards on their web sites. And I went to the RIAA web site and not only didn't find any techical information, I couldn't find a phone number so I could speak to a human. I realize that this is a minor point for the most part but I just thought I'd let you know what I had found. Thanks for posting your info and providing the public service. David Hood MST Bragg

1/4" or Phone Connectors

These are the big-brothers of the miniature stereo plugs that are found on Walkmen and smaller mini-compo systems. They are found in one long shaft 1/4" in diameter. Along the shaft there are divisions of plastic that separate the contact points along the shaft. There is also a little constriction in the shaft that permits a 1/4" connector to lock into a jack when inserted, though this is nowhere as secure as an XLR locking clip. Since they are usually used for headphones, they are also called Phone connectors.

1/4" Connectors come in two-contact and three-contact connectors. I have seen a four-contact connector somewhere before, but I can't remember where. Two-contact connectors are strictly mono-unbalanced connectors. Three-contact connectors, often found on larger headphones, could either be used for stereo-unbalanced connections or mono-balanced connections.

Two-contact connectors are commonly termed as TS connectors, as the shaft is divided into two parts: the Tip, and the rest of the connector, known as the Sleeve. The constriction in the shaft is part of the tip in both two- and three-contact connectors. The tip is usually used for the signal ('hot') and the sleeve is used for shielding and the signal return ('cold' as well as 'ground').

Three-contact connectors are known as TRS connectors. The shaft has an additional plastic division in would have been the sleeve in a two contact connector. The contact closer to the tip is known as the Ring, while the contact closer to the cable is known as the Sleeve. The Tip is the 'Hot' connection, the Ring is the 'Cold' connection, and the Sleeve is the 'Ground' connection in balanced TRS connectors. For stereo connectors, the Tip and Ring are both the 'Hot' contacts for the left and right signals respectively, while the Sleeve is both the 'Cold' and 'Ground' for both sides.

1/4" connectors are usually male, and jacks are usually female. Interconnection between two cables usually require a female-female adaptor (a little cylinder to whole two shafts).

A variation of the stereo 1/4" connector is found in the Y-splitter. This consists of two unbalanced cables connected to one TRS 1/4" connector. Instead of carrying left and right signals, the Y-splitter carries one signal into a jack and another signal out. This is used in mixer inserts, in which a signal is tapped out of a mixer for processing with equalisers, echo units, and other processors, then put back into the mixer to continue the signal path. With a Y-splitter, the 'pulling out' and 'putting back' of a signal can be achieved with one TRS jack.

Some 1/4" jacks have a special feature that, as far as I know, can only be found on mini-phone jacks as well. This type of jack is known as the break-jack. One example of its use can be seen in some stereo systems, in which the insertion of a headphone (1/4" connector) results in the cutting-off of the main loudspeakers. This jack has a slightly more complex design, but basically it permits a signal to travel in one set of paths, or you can insert a 1/4" connector and have it travel through the connector while cutting off the original set of paths. Thus, a connector inserted into a break-jack becomes both a switch and signal connector at the same time.

It is possible to 'tap' or 'sniff' a signal out of a break-jack without cutting off the original flow of signal by partially inserting the connector into a break-jack, such that it doesn't 'click' into place. Of course, this means that a little jarring will cause the 1/4" jack to fall out of place, so this practice isn't really recommended.

There's a whole range of different manufacturers for TS and TRS 1/4" connectors out there. I prefer the cable brand Canare, which is mostly metal. I prefer these because, if you slip with the soldering iron, you don't inadvertently melt any plastic parts. There is also a good spring type cable support which prevents cables from bending too sharply as they come out of the connector, and a supplied little plastic tube with each connector that prevents the soldering joints from coming into contact with the shield. They are a little on the large side, which might be a problem in some cases, but have generous room inside the connector for soldering.

Some people prefer plastic-clad connectors, since you can't get electrocuted from just holding the connector (very very rare...it means your shield is carrying a major current), the shields of adjacent connectors cannot accidentally touch (leading to ground loops) and they are cheaper and lighter. I've found them to be less durable and difficult to re-solder if you want to reuse pieces, but use what you prefer.

RCA/Phono Connectors

These are the most common connectors in home hi-fis, CD players, LD players and Videocassette recorders. They are simple in construction and are strictly unbalanced. RCA jacks are a small cylindrical stub with a hole in the middle. RCA connectors have a small pin about 2-3 mm in diameter with a cylindrical 'flower' of metal around it. Connectors are typically male and jacks are typically female.

RCA jacks and connectors have an inner contact (pin-to-hole) and outer contact (flower-to-cylinder). The inner contact is for the 'hot' signal and the outer contact is for both the 'cold' and 'shield'.

RCA jacks are typically used for carrying -10dB line-signals, although they are also employed for phonographs/turntables, which is why RCA jacks are also known as Phono jacks. Don't get these mixed up with Phone jacks! They could also quite possibly carry +4dB signals, although this is rarer.

RCA connectors are known to be a little less reliable than 1/4" and XLRs, especially the plastic pre-made type. They are not designed for heavy-duty use, although some more expensive RCA connectors can last quite a long time. For example, Monster Cable builds a special type of RCA connector that has a slitted turbine-like flower that is ridiculously difficult to remove and insert (which was the point in the first place) while Canare's all-metal RCA connectors are almost as long as the 1/4" connectors they make, putting a little more stress on the jack than the connector. Although RCA connectors are easily dented, they are also easily bent back, although I wouldn't recommend using a damaged connector for a long period of time, as it would probably fail again unexpectedly.

I personally find 1/4" connectors easier to solder than RCA connectors, as the RCA connector would typically use a mix of the 'needlehole' solder joints (common in 1/4" jacks) and the 'spade' type of solder joints (common in XLRs). I like 'needlehole' joints as long as your cables are clean and well trimmed, otherwise they would just be too fat to fit in the needleholes for soldering.

RCA connectors range from the super-cheapo flimsy plastic whatsits to the mega-expensive overkill metal and space-age composite things in audiophile shops. Buy according to your needs, don't go overboard: the difference in sound quality will probably be nearly inaudible. For almost-permanent setups, the cheap, pre-made cables will be sufficient. For setups that require constant changing and rearrangement, you may want to spend a bit more on something that doesn't weaken or rust easily.

RCA connectors are also used in digital audio as the jacks for digital coaxial cables. These are usually slightly higher quality with gold plated terminals. Composite video can also be carried over RCA connectors, so most VCRs and TV sets should be able to support both sound and video being carried over separate RCA cables. These cables are usually color-coded with yellow being the video connector, white or black being the stereo-left sound connector, and red as the stereo-right audio connector. In a pinch, a stereo pair of RCA cables can be rushed into service for video and mono-audio, with little or no difference in either audio or video quality.

Mini-phone connectors

Named because they are used most commonly for miniature earphones, these smaller versions of the 1/4" connectors require the least space of all the popular connectors. They are ubiquitous on Walkmen, Discmen, Watchmen, Camcorders, PC sound cards, Macintoshes and other portable audio or video components. Really small music sequencers, such as the Yamaha QY10, also utilise these connectors.

These connectors are really unreliable. The springs in the jack have been known to give up after a dozen insertions and removals on budget equipment. They should only be used on really small equipment, and if possible, on connections that need not be removed and re-inserted often.

It is thought that these components are harder to solder than RCAs, but I've found them about the same difficulty. Internally, the joints in a mini-phone connector are not much smaller than RCA solder joints. Like their big brothers, they also come in plastic and metal versions. The plastic versions tend to melt a little when soldering and are practically unuseable if you try resoldering new cables to it twice.

They come in TRS connectors and TS connectors. The joints are exactly the same in positioning as the 1/4" version, and break-jacks are also possible for mini-phone jacks.

Mini-phone jacks are also used for Plaintalk microphones on Macintoshes, but these are slightly longer in length. Although they are TRS jacks, the contact points serve slightly different purposes. Most importantly, the tip of the Plaintalk connector is used to draw power out of the Mac to power electret Plaintalk microphones. Dynamic microphones and line-level TRS connectors can also be used in a Mac, as they are not long enough to reach the contact point that supplies power. Condensor microphones have to draw their power from somewhere else, maybe a battery pack.

Other connectors

That's it for the whole list of common connectors for analogue audio signals. There are a few others that aren't as common, but have been seen used in enough in equipment to warrant a mention.

Banana Plugs

These connectors are just a more flexible alternative to bare wires. Typically, they only have one big conductor, which is a pin with several flat springs on the side. A banana jack is just a hole, in which the banana connector slips into and fits snugly. It is less prone to fraying than bare wires and simple to use for quick installations and deinstallations. It can usually withstand light tugs, but a hard jerk would definitely pull out the connector from the jack. Certain bare wire jacks (the screw-tight type) also have a hole in the middle of the screw to accomodate banana plugs. As far as I know, they are only used for speaker cables.

Leads/Bare Wires

The simplest type of connectors, usually only seen on speaker cables. Bare wires can be connected either by screwing down a jack so that the cable is held tight, or by inserting the wires while holding down a spring-loaded catch which would grip the wires tight when released. Bare wires have a tendency to fray and break after repeated use. Soldered wire leads don't fray as easily, but screw-tight connections might lose their tightness after time, as solder still flows even when cold, at a much slower speed, of course, than liquid solder.
Leads are shaped pieces of metal soldered to the ends of cables. They are just designed to overcome the fraying problems of cables. Two types of leads are the 'spade' and the 'clamp'. The 'spade' looks like a blunt two-toothed fork, designed to fit in screw-tight jacks. 'Clamps' are common on batteries. The 'clamp' jack is just a flat piece of metal. The 'clamp' connector is a metal piece in the shape of a horizontal 'B' meant to grip the jack tightly.

Speakon Connectors

This is a new, heavy duty type of connector designed specially for speaker cables, because of the heavy power loading of such applications. They are highly secure and made of plastic, in order to prevent shock hazards from touching the connectors. To secure a Speakon connection, you must insert the Speakon connector to a Speakon jack, twist the Speakon connector about 45°, then tighten a ring around the connector that forces the connector towards the jack. As such, the cable would probably be severely damaged by a strong cable jerk before the Speakon even begins to budge.

I've tried soldering them, but it's almost impossible, as the contact points are surrounded by plastic and melting the plastic is unavoidable. To utilise them, there are hex screws on the side in which you tighten onto bare cables. The hex screws are tiny, so you might need to get a special Allen key to tighten them. I usually use bare wires, without tinned/soldered tips, as I don't want the tightening to weaken after time. They are designed to last a long time.

Digital Signals

Digital signals are communicated from machine to machine typically as a series of pulses of 'on' or 'off' signals, high voltage or low voltage signals, instead of a continuous fluctuation like analogue signals. Digital cables are usually short. When they are metal, they could be high-quality OFC, silver or even gold cable. Graphite cables are also sometimes used for digital signals.

Digital signals are usually electrical, and they use much the same type of connectors as analogue signals. Again, the connectors are of higher quality, for instance, they might be gold-plated. RCA, mini-phone and XLR connectors are frequently used for digital connections.

However, digital signals might be optical. A small laser Light Emitting Diode at the output end of a digital audio component and a small Light Sensitive Resistor at the input end allow blinking lights to be transferred down optical fibers. Of course, light is hardly affected by the electromagnetic radiation of a typical room, so corruption of the signal is even less of a possibility. The connectors used for fiber optics would have one transparent end, that fit inside special jacks in the audio components.

The question is, with the supposed higher resistance to corruption that digital signals are supposed to have, why do they require such higher quality components? Perhaps it is due to the fact that unlike analogue signals, a partial loss of digital information would effectively render the whole signal being unuseable. A partial loss of analogue signal would either result in a lower S/N ratio, or a loss in the high frequency part of the sound, but the sound might still be useable.

See the category on Digital Audio for more information.

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