By Paul Kimbrel
One of the most intimidating things about a studio (aside from those behemoth mixing boards) is the mass of cables and connectors that one acquires over the years. In most studios and live sound platforms I’ve been involved with over the years, the cable and connector management has been abysmal at best. My studio is no exception.
But cables and connectors are the life blood of any studio. And there is no shortage of varieties when it comes to cables. Especially in the digital era. The old stand-bys remain the same… line cables, balanced cables, RCA jacks, phono jacks, XLR jacks, etc. But we now have fire-wire cables, USB cables, etc.
The focus of this section is to give you a primer of the basic studio cables and how they operate in the studio setting. Some cables can even be used in multiple, but extremely different ways in the studio. This section falls most decidedly in the “technical” aspect of sound.
“Signals” refer to the alternating current (AC) the moves from device to device in the studio. This AC electricity alternates at the same frequencies and relative power as the sound waves we are storing and manipulating. Often times, the electrical signal passing over the wire is referenced in the studio nomenclature as sound itself, even though the signal doesn’t really become sound until it passes through a speaker.
Signals can be transferred from one device to another in a variety of ways. Signals in the form of AC electricity are knows as “analog” signals. These electrical signals can also be converted into digital pulses and transferred from devices to device, too. However, the focus of this section will be on analog signals.
Balanced vs. Unbalanced
When a signal is sent from one device, such as a microphone or guitar, to another device, such as a mixing board, it can encounter a variety of problems on its journey. A long wire that connects devices together can actually act as a radio antenna, picking up signals from radio transmitters, cosmic rays, electric lights, even people. These extra signals, called interference, can actually mix with the desired signal as it is traveling over the wire.
If the original signal is strong enough and the cable through which it is traveling is shielded well enough, the relative volume of the interference it receives can be very small to the point of not existing (for all practical purposes). However, when dealing with extremely weak signals, such as signals from a microphone, the interference can be loud enough to be heard along with the original signal.
Cables and connectors that do not deal with the interference are very simple. They often have a single conductor that carries the signal, and a second conductor that completes the electrical circuit between devices. These cables, connectors, and even the signal they carry are know to be “unbalanced.”
What does that mean exactly?
Well, to understand that, you must understand what it means to be “balanced.” Cables, connectors and signals that are know to be “balanced” operate in the following way: Before leaving the original device, the signal is split into two identical signals. One signal is sent down a wire to the other device unaltered, while the other signal has it’s polarity reversed.
To “reverse the polarity” of a signal means that when the original signal moves in a “positive” direction, its copy moves in a “negative” direction in the exact same proportion as the original. What you end up with are two signals that are identical, but one is “upside down” compared to the other.
Now, that “upside down” signal is sent down another wire to the other device in parallel with the wire carrying the unaltered signal. Any interference that these signals encounter will effect them both in identical ways. If there’s a spike to the positive direction, they both get that spike in the positive direction (and vice versa).
Once the two signals reach the next device, the altered (”upside down”) signal is flipped again to make it the same as the original signal. It’s mixed with the unaltered signal to recreate the original sound. However, when that “upside down” signal is made “right side up,” all the interference it encountered is turned “upside down.” When the two signals are mixed, the interference will actually cancel itself out into nothing.
This is known as a balanced signal. Balanced cables and connectors tend to be much better at keeping interference out of the signal path. However, they require two conductors to transfer the signal from one device to another (plus a third to complete the circuit).
When looking at unbalanced connectors, you will notice that there are always two connecting points. One for the signal, one from the “ground” (used to complete the circuit).
Typical connectors used for unbalanced signals are quarter inch jacks with two connectors (called “tip-sleeve” connectors) and RCA connectors. The “tip”, or “center” of these connectors carry the signal, while the “sleeve” or “shield” connects the ground.
Often times, unbalanced cables are combined together to carry two different signals at the same time. These are known “stereo” cables. The connectors used to hook up the two different signals to a device can be separate, in the case of RCA connectors…
…or they can be combined into a single connector. An example of a connector that can connect two signals to a device is a quarter inch jack with three connectors (also called “tip-ring-sleeve” connectors – “TRS” for short). The two connectors towards the end of the connector, the tip and the ring, carry the two signals. The sleeve still connects the ground.
TRS connectors are sometimes called “stereo jacks.” However, I try to always refer to them as TRS because they can actually serve to carry a single signal as a balanced connector.
When looking at balanced connectors, you will notice that there are always two connecting points. Two for the signal (positive polarity, negative polarity) and one for the ground (to complete the circuit).
Two pins of an XLR connection is used to carry the original signal, and the second is used to carry the reverse-polarity signal. The third connects the ground.
TRS jacks can also be used to carry balanced signals. In this case, the tip and the ring carry the nominal and reverse polarity signals. The sleeve still connects the ground.
Be aware of the context in which this connector is used! You do not want to hook a stereo connection to a balanced connection! Depending on how things are used, you can cause severe damage to your equipment!
Adapters are a necessary evil in a studio. Invariably you will have two devices that have incompatible connectors, but can handle the same signal. Adapters make it possible to connect the two.
Most adapters are no-brainers. If you need to go from a “little” connector to a “big” connector (eighth inch to quarter inch), you get a little-to-big connector. If the connection points are a single signal, you get a tip-sleeve little-to-big. If the connection points are dual signal (stereo), you get a TRS little-to-big. Etc. Etc. Etc.
However, here are a few connectors that are off the beaten path, but I’ve found invaluable in the studio:
1) Monaural-to-stereo (and vice versa).
These adapters look to have the same “input” connector as its “output” connector. However, they are built to accept a tip-ring connector and they produce a TRS connector. The reverse is also available.
2) Balanced-to-unbalanced (and vice versa).
Unfortunately, there are several situations where you have to manually switch between balanced and unbalanced signals. Perhaps you have a guitar that you need to plug directly into your mixing board, and your mixing board only has XLR connectors.
Balanced/Unbalanced adapters work both ways by both splitting out an unbalanced signal into it’s balanced counterpart, and by combining a balanced signal back into an unbalanced signal. The short name of these adapters are “baluns.” They come in sorts of sizes and shapes. Guitar players are often familiar with the “direct box.” Direct boxes are basically big bulky (I mean “sturdy”) baluns. Radio shack sells compact baluns where one side of the adapter is an XLR connector and the other is a quarter inch jack (in various configurations).
You need to have at least two, of not more of these in your studio – for each direction. I personally, have about eight Radio Shack baluns, and two direct boxes, and I have put them all to use at one time or another (both in the studio and out in the field).
I don’t know why, but I’m always reaching for an RCA-to-Tip-Ring adapter. I don’t think I have very many RCA based connections in the studio, but invariable, I’ll use one. My consumer cable pile is full of RCA stereo cables, so that’s probably why.
4) Insert Cables
Insert cables are basically the cable version of a “Monaural-to-stereo” adapter. However, they tend to have all male connectors (use your imagination here) where one TRS connector splits into two tip-ring connectors. I get more use out of these cables than anything else in the studio.
They’re called “insert cables” because they’re used to “insert” a device into a signal chain. I’ll talk more about this when I discuss signal path.
Adapter Hell (OMG - he said 'hell'!)
Beware adapter h-e-double-hockey-sticks! It’s an evil place (HA!) where three, four, even five adapters get chained together to go from an XLR connection to an eight-inch stereo jack. I created monsters such as that in my earlier studio, and frankly, I wouldn’t have been able to record without them.
But they are ungainly beasts! They will short out when you least expect them to! You’ll start performing “the roll.” The roll is where you twist the adapters around, cracking and popping all the way around until you find the “sweet spot” – the place where all the adapters connect and harmonize as one.
Or you’ll curse and spit and turn and turn and curse some more until you’ve broken off the eighth-inch jack inside your computer.
Yes. Yes I have.
Learning to solder in these instances is a good trade to have under your belt. Having a single adapter that, say, goes straight from XLR to eighth-inch stereo would be a good adapter to have, but you’re never going to find one on the market. So buy the parts and build the adapter yourself. Don’t worry if it looks like crap. As long as it works, no one will know the difference.
Bear in mind that going from a balanced signal to an unbalanced signal is not as easy as connecting point A to point B. The simplest way to create a balun is to use a 1:1 transformer. These are transformers where the primary and secondary windings contain the same number of turns. Going into why these balance and unbalance signals is more involved than I wish to describe, suffice it to say, they do the trick. And 99% of all direct boxes and XLR adapters use these transformers to convert signals.
As far as how you go about hooking them up is tricky, but not too complicated. Personally, I used the schematic on the side of one of my Radio Shack adapters and it worked well.« The Basics | Table of Contents | Output »