Suffering from mysterious hums and buzzes in your studio? This down‑to‑earth explanation will help you identify and solve the problems — or hopefully avoid them in the first place!
Some of the most frequent calls for help in the Sound On Sound Forum concern unwanted hums or buzzes emanating from studio monitors, usually with a statement that “it’s something to do with grounding.” That assumption is usually right, too — it often is something to do with grounding! But there are many ways that incorrect grounding/earthing can cause problems, and different fixes are required for different issues. It’s also possible, of course, for there to be multiple different grounding issues within the same system at the same time. Figuring out the problem(s) requires some understanding of what grounding/earthing is supposed to do, as well as how different equipment is designed to be earthed (or not). But with the right approach, it’s usually straightforward to work out the most effective way of interconnecting different kinds of equipment correctly and, even more importantly, safely. That last point really cannot be overlooked — people have died trying to fix grounding problems in some really stupid ways!
Solving grounding issues only requires a little basic fact‑finding about the equipment involved, a plan of what’s connected to what, some logical thinking and, it must be said, plenty of persistence and patience. It can often be a confusing, frustrating and iterative process, but I guarantee that following the concepts and techniques I explain below will eventually get you there.
Most unwanted noises in an audio system are caused by some form of external electrical interference getting somewhere it shouldn’t. Sometimes that interference gets in via the mains cable, but often it’s picked up as RFI (Radio Frequency Interference), so let’s deal with that problem first.
The Faraday Cage
The best preventative solution for RFI is to protect sensitive electronics within a conductive box. This is called a Faraday Cage (or Faraday Screen) and derives from the work of Michael Faraday in 1836. In essence, it’s nothing more than a conductive (metal or metalised) enclosure, which naturally stops varying electromagnetic fields (like radio transmissions) from passing in or out.
Audio equipment, like effects processors, mixers, interfaces and microphones, usually has a metal case that serves as a Faraday Cage, protecting the audio circuitry inside from external interference. A Faraday Cage doesn’t have to be solid metal, either; a metal mesh works too, provided the holes are smaller than the wavelength of the highest radio frequency to be excluded. Screening the electronics inside a unit is great, but the signals coming in and going out need protection from interference too. To that end most cables have a conductive outer shield of some type enveloping the signal wires, and that shield is normally connected to the equipment’s metal enclosure when the plug is inserted. In this way the cable shield extends and links the Faraday Cages of devices when they are connected together. Although a Faraday Cage doesn’t necessarily have to be earthed (grounded) — it isn’t in the case of an aeroplane, for example — most are earthed, for reasons I’ll explain shortly.
Putting this into a practical context, consider a balanced microphone connected to a battery‑powered digital recorder. The metal case of the recorder forms a Faraday Cage protecting its electronics, and that Faraday Cage is extended by the shield of the mic cable to the microphone itself, where it is connected directly to the mic’s case and pop‑shield grille. External interference is therefore kept out of harm’s way as the Faraday Cage protects and envelops all of the mic’s and recorder’s circuitry and associated wiring. As the recorder is battery‑powered there is no direct connection to earth in this system (eg. via a mains cable) and so the setup is said to be ‘floating’ (in respect of earth). Nevertheless, it works perfectly without being earthed, as the audio signals pass from mic to the recorder entirely protected within a Faraday Cage and thus free of interference.
But what happens if the balanced microphone is replaced with an unbalanced electric guitar? The guitar’s electrical components aren’t normally protected inside a metal box — they’re just crammed into a hollowed‑out plank — and the signal voltage generated by the pickups isn’t passed to the recorder via a pair of (balanced) wires safely protected within the cable’s shield. Instead, the shield itself is employed as part of the (unbalanced) signal’s circuit path.
Electrically, this arrangement looks very much like a TV aerial, so instead of the recorder’s input circuitry looking for a signal voltage between two wires protected inside a Faraday Cage, it instead receives a signal voltage established between one signal wire and the Faraday Cage itself. Consequently, any interference picked up by the Faraday Cage is automatically added to the guitar’s signal voltage (because they share the same circuit pathway). That’s why unwanted hums and buzzes are a very common problem in this kind of scenario.
What can be done to improve matters? Well, we could give the interference somewhere better to go than into the recorder’s electronics — like a nice solid, clean ‘earth’. The magic of the ground/earth is that it is a very large conductor that sits at zero Volts, and it is almost impossible to change that potential. So anything connected to earth will effectively be clamped at zero Volts. If the Faraday Cage is earthed, any interference it picks up will flow as current straight into the earth, and the recorder’s electronics can now look for a signal voltage measured between the signal wire and the zero Volts of a clean earth.
Unfortunately, while earthing reduces interference collected by the Faraday Cage, the rest of the guitar’s electrics are still a virtual TV aerial. But using copper foil (or conductive paint) to create a Faraday Cage around this circuitry inside the guitar’s control cavity really helps to minimise the amount of interference getting into the control and switch wiring.
Groundless Laptop Studios
Studio DAW setups using laptop computers (or tablets) are typically also ‘floating’ systems lacking a solid earth. With balanced audio connections they can work perfectly well, but they often suffer in exactly the same way as the example above when connected to unbalanced equipment. Not surprisingly, then, providing a solid earth connection to the laptop’s audio interface often removes troublesome interference problems completely — and it’s easy to do.
The most convenient way of providing a good earth is simply to connect a device which has a protective earth connection via its mains cable. For example, most powered monitor speakers are Class I devices (see the ‘Classy Power’ box) with a protective earth, and that is normally extended back to the interface via the shields of the balanced audio cables used to connect them. So, just plugging powered monitors into your interface can provide the solid earthing needed to stop the system humming or buzzing. Connecting any other Class I audio device — a keyboard, an external signal processor, a guitar amp (they don’t have to be switched on, just plugged in to the wall socket) — will work just as well. Having said that, having multiple earth connections can lead to another problem, as I’ll explain shortly!
If suitably earthed external equipment isn’t available, a dedicated earth connection can be provided instead. A safe way to do that is to use a dedicated earthing plug such as that made by Groundology, and I’ve described this arrangement in this article: www.soundonsound.com/reviews/groundology-earth-connection-plug. Groundology sell suitable earthed mains plugs for most parts of the world, but if looking for alternative suppliers don’t be tempted to use the kind of earthing plug intended for static protection, since these have a built‑in high‑value resistor to restrict static discharge current flow and that’s not appropriate for this application. The Groundology plugs provide a direct low‑impedance connection to the protective earth terminal of the mains wall socket, and they can be wired to the sleeve terminal of a standard jack plug. Inserting that plug into any convenient socket on the interface provides a solid earth for the interface, allowing interference collected on the Faraday Cage to go direct to earth.
When Is Ground Not A Ground?
Given what I’ve said previously about the Earth’s zero Volts potential, it seems logical to assume that all ‘earths’ or ‘grounds’ share that same ‘zero voltage’. Unfortunately, the reality is that they don’t... and therein lies the root cause of most ground‑loop connection problems!
The reason all grounds are not all the same lies in the wires we use to connect them. All electrical conductors have some inherent self‑resistance (and capacitance and inductance). Consequently, as soon as any current flows within the conductor, a voltage also develops along it, according to Ohm’s Law: V=IR — the current (I) flowing in the cable, multiplied by the cable’s internal resistance (R), results in a voltage (V) being generated along it.
Of course, the resistance within a cable is usually extremely small (milli‑Ohms), but it still results in a small voltage being developed when a small current is flowing. This is significant because audio signals are, themselves, often quite small voltages (usually measured in milli‑Volts). So, it doesn’t take much current flowing in a sensitive ground path to generate audible hums and buzzes! What do I mean by a ‘sensitive ground path’? Well, the electronic circuitry in most audio equipment works with unbalanced audio, where the signal voltage is measured relative to a ‘reference ground’ (see Diagram 1). Consequently, any noise currents passing along that reference ground will intermingle with the wanted audio currents, inherently adding unwanted noise to the audio signal. So, it’s critical that noise currents are kept away from the audio reference ground. This is achieved mostly through good equipment design and situationally appropriate interconnection techniques.
Grounds: How Many Is Too Many?
The most common ‘grounding problem’, historically, is due to noise currents arising from ‘ground loops’ getting into equipment via the protective earths of their mains power connections. It’s often simplistically described as having ‘too many earths within a system’, but there is nothing fundamentally wrong in having multiple earth connections if the audio equipment and its interconnections are designed and implemented correctly. Well‑engineered studio installations all around the world confirm that fact. However, equipment isn’t always designed or connected ideally, so we need to take pragmatic measures to deal with flawed systems.
Ground loops mostly involve Class I mains‑powered equipment — that’s equipment with a protective earth connection via the mains cable (see ‘Classy Equipment’ box). If the equipment is battery‑powered, or Class II, or powered using a low‑voltage external supply, it’s unlikely to play any role in a suspected ground‑loop problem. This is why it’s important to identify the type of equipment being connected when trying to resolve ‘grounding problems’.
So, what is this mysterious ground loop? Consider a simple bedroom studio with several mains power outlets on different walls around the room. The mains wiring inside the wall linking those sockets back to a Consumer Unit will be many tens of metres in length, and with such long cables there will inevitably be small but measurable resistances between the terminals of different wall sockets.
In a perfect world, there would be no current flowing along the protective earths of the in‑wall mains wiring and, if there’s no current flowing through the cable’s resistance, the earth terminals in every wall socket would be at exactly the same (zero) voltage as the power station’s local earth rod sunk into planet Earth. However, in the real world most mains‑powered devices have mains filtering circuitry and/or a mains transformer, both of which introduce capacitance between the live, neutral and protective earth connections. Mains power is AC (Alternating Current) and so those small capacitances allow a small AC current to leak through to the protective earth. Consequently, mains‑powered devices plugged in around the building all contribute small leakage currents into the protective earth wiring. This is entirely normal and perfectly safe, but the issue for us is that those small leakage currents create small voltages along the tens of metres of in‑wall wiring, meaning that the earth terminals of the mains outlets on different walls will acquire slightly different (non‑zero) voltages.
So, we have various Class I mains‑powered audio devices plugged into different sockets around the room, and that equipment is interconnected to pass audio signals. Remember, the audio cable shields are normally connected directly to the equipment’s protective earth too, so just by plugging this equipment together and into the mains sockets we have created a ‘ground loop’ (see Diagram 2).
As we already know, then, there’s likely to be a small voltage difference between the earth terminals of the different mains outlets because of leakage currents and cable resistance. The mains outlet with the higher voltage will force a small current to flow from that wall socket’s earth terminal into the associated audio device (A) via its mains cable’s protective earth. From there it travels along the (red) audio cable screen to the second audio device (B); and then via its mains cable’s protective earth into its own local mains wall outlet. The current then flows back to the first wall socket via the building’s in‑wall wiring. Hence a classic ground loop — it’s inevitable given the way we normally power and connect equipment in a studio.
Stars & Daisies
Most studios have more than two mains‑powered devices, of course, and multiple plug boards are typically needed to provide additional mains sockets. However, since everything plugged in is likely to leak a small current into the plug boards’ protective earth wiring, small voltages can still develop, leading to different earth voltages in different plugboards. That situation is greatly exacerbated if the plug boards are connected in a daisy‑chain, but minimised if they are connected in a star arrangement, thus greatly reducing the chances of ground‑loop problems (see Diagrams 4 and 5).
Noise Currents Inside Equipment
I’ve said repeatedly that well‑designed equipment using balanced audio connections isn’t affected by circulating ground‑loop currents, but in poorly designed equipment ground‑loop currents can find their way into the audio reference ground to create audible hums and buzzes — hums because the noise current is derived from the 50 or 60 Hz mains supply, and buzzes because of the related harmonics that accrue on mains supplies.
Diagrams 6 and 7 illustrate part of a mixing console or audio interface. I’ve shown several transformer‑balanced inputs feeding high‑gain amplifiers (the yellow triangles). The amplifier outputs might feed output transformers (as here), or be mixed together, or be converted to digital — it doesn’t matter for the purposes of this example. What does matter conceptually for this example, though, is that the input transformers convert between the balanced external connections and the unbalanced internal amplifier circuitry, which measures audio signal voltages against the reference audio ground (shown in green). The red loop represents the audio signal current path around the amplifier circuitry, while the blue line shows the external noise current path from the input connection going to earth. We’ve met this situation before...
As you can see in Diagram 6, the reference grounds of each input channel are connected to a ‘star ground’, which is itself earthed via the mains cable’s protective earth connection. However, in this ‘bad’ design, the ground‑loop or RFI currents carried on the input cable shields pass through the audio reference grounds of each channel’s amplifier on their way to that star‑ground point. Consequently, unwanted ground noise is inherently added to the wanted audio signal within each channel. A lot of traditional audio mixers were built in exactly this way, with pin 1 of the channel’s XLR wired straight into the mic preamp’s ground (simply because it was convenient). This has become known as the ‘pin 1 problem’ and much has been written about it in professional audio circles!
Avoiding this catastrophic problem is remarkably easy, as shown in Diagram 7: noise currents on the cable shields simply require a separate route to earth, bypassing the audio channel reference grounds. This is shown in the diagram below, in which the ground‑loop and interference currents from the cable shields at the inputs are kept completely separate from the audio reference grounds, so can’t get into the audio amplifier circuitry at all. This arrangement is typically achieved simply by bonding the shield terminals of the input (and output) connectors directly to the equipment’s metal enclosure, maintaining the Faraday Cage concept discussed earlier.
So, by using balanced connections and constructing equipment sensibly, noisy ground currents are kept well away from the audio circuitry, and thus ground loops and external interference aren’t problems at all. But what do we do with equipment that isn’t well‑designed, or when using unbalanced connections? In these situations, the best approach is to prevent the noise currents from entering the equipment in the first place, for example by breaking the ground loop.
The protective earth cannot be disconnected in equipment power cables or their mains plugs — such outrageous ‘solutions’ have killed a lot of guitarists over the years!
Clearly, there are several places where a ground loop could be broken — but many of them are fundamentally unsafe! For example, disconnecting the protective earth at the mains wall sockets is obviously not acceptable, since it would defeat a primary safety provision. For the same reason, the protective earth cannot be disconnected in equipment power cables or their mains plugs — such outrageous ‘solutions’ have killed a lot of guitarists over the years!
There are many safe and simple alternatives and the easiest, often provided by the manufacturers of Class I equipment, is a ‘ground‑lift’ switch. Class I equipment normally has a direct connection between the internal audio reference ground, the equipment’s metal chassis, and the mains cable’s protective earth — usually at a star‑ground point. A ground‑lift switch simply disconnects the audio reference ground from that star‑ground, allowing it to ‘float’. In this way noise current trying to get to the protective earth via the audio reference ground (as in the ‘bad’ equipment example above) no longer has anywhere to go — the ground loop is broken. Note, though, that the equipment’s metalwork is still safely earthed via the protective earth connection in the mains cable.
If a ground‑lift switch isn’t available on a Class I device, the next easiest option is to interrupt the audio cable’s shield connection in some way, and this approach also works if the noise currents are due to RFI. (This won’t work for phantom‑powered microphones, as the shield connection forms the 48V power supply’s return path.)
The cable shield connection can be severed simply by opening the connector, cutting the screen connection inside the plug, and isolating it with insulating tape. This only needs to be performed at one end of the cable (usually the destination/input end) and it’s an arrangement often referred to as ‘one‑end‑only’, which was a backbone of much professional studio installation wiring. If you do cut the shield connection, do remember to mark the cable in some clear way, to avoid it being re‑deployed later in a situation where the shield connection is required!
With balanced interconnections, the shield plays no role in transferring the audio signal, so breaking that connection doesn’t affect the audio, just unwanted shield noise currents. The same cannot be said of unbalanced connections, though, and alternative solutions are required for solving ground loops with unbalanced equipment (see below). The one‑end‑only solution is also not applicable with battery‑powered and Class II equipment, as the cable shield is used to share the signal ground reference.
If you’d rather not hack your cables, a more versatile though more expensive solution is to employ an audio isolation transformer box. The 1:1 transformer passes the audio signal as a varying magnetic field across the transformer’s windings without any direct electrical connections (including the shield) between the box’s input and output sockets. This breaks a ground loop, and prevents RFI currents from getting into the receiving device (Diagram 8). Audio isolation transformer boxes are available in various formats and prices from numerous manufacturers, and although ultra‑low‑distortion transformers are quite expensive, modestly priced options are often perfectly acceptable. For instance, I routinely use ART’s DTI isolation box for identifying and resolving ground loops and related problems. It offers two channels with a plethora of connector formats, making it very convenient and versatile to integrate quickly into any system with balanced or unbalanced connections.
When I suspect a ground loop or shield interference problem I usually employ a transformer isolation box to test my theory. If the unwanted noises go away when the box is inserted, I know they were due to noise current on the shield connections. If practical, I would usually then remove the isolation box and cut the original cable shield(s), marking them accordingly, because it’s a much less expensive solution than permanently installing a transformer box, while also avoiding any possibility of a transformer degrading the sound quality. If the noises don’t go away with the isolator box connected, I know the problem lies elsewhere!
Unbalanced Sources
The transformer isolation box is particularly helpful in resolving ground loops with unbalanced Class I sources (like some vintage synths). But if the unbalanced source is connected to a balanced input (like in a mixer or interface), another option is a ‘pseudo‑balanced’ cable. Unfortunately, and despite their immense usefulness, I’m not aware of any commercial cables wired to this format, but bespoke cable‑making services can construct them to order, and they’re an easy DIY build for anyone familiar with a soldering iron.
A standard balanced cable (two‑core plus shield) is used, with the balanced destination end wired as normal with a male XLR or TRS plug. At the unbalanced (source) end, the hot signal wire is connected to the unbalanced signal output (the tip of a jack plug, for example), while the cold signal wire is connected to the plug’s shield (sleeve) terminal. In this way the source’s signal voltage is passed directly to the balanced input, but there’s no connection between the source’s ground and the destination ground — hence no ground loop. The cable’s shield is connected at the balanced destination end but left isolated (and insulated) at the unbalanced source end.
Many of my synth cables are built in exactly this way, and work perfectly well. However, the unterminated cable shield is effectively acting as an aerial to pick up local interference — if that’s a problem, then better RFI protection can be achieved by connecting the cable shield at the source end’s plug sleeve terminal via a small capacitor. The value isn’t critical; anything under 100nF that fits inside the plug body will be fine.
Alternatively, a low‑value resistor can be used to maintain some RF screening while reducing any ground‑loop currents to inaudibility. 100Ω is a typical value in this application, but again it’s not critical. If you have a large enough connector body, the resistor and capacitor can be used together in parallel.
It’s important to note that a transformer isolation box and/or pseudo‑balanced cable are only appropriate if the unbalanced source is a Class I device. If these options are employed with Class II devices, or those powered via wall‑wart PSUs, they are more likely to create problems than to fix them! This is because such devices rely on receiving a ground reference directly from the destination device via the connecting cable’s shield. Intentionally interrupting that ground connection leaves the source floating and acting as an aerial to collect and inject unwanted RFI.
Plan It: Earth!
So, I’ve described some practical solutions for a variety of ‘grounding problems’ but how should they be deployed? I mentioned earlier the importance having a clear and detailed plan of how the entire system is connected together. I like to sketch it out on paper, with a note on each device identifying whether it’s Class I (safety‑earthed), Class II (double‑insulated), or battery‑powered and, ideally, where each unit is powered from (which wall socket or mains distribution board).
The plan should also show all audio connections between devices (multiple channels between two devices can be shown as a single thick connection for the purposes of ground loops), and specifying which connections are balanced or unbalanced. Include digital audio, digital clocking, USB, FW and TB connections, too. Although it is helpful to include ADAT, optical SPDIF and MIDI connections as part of the system overview, these are all optically isolated and can’t contribute to ground loops or RFI. All the others (bar a few specialist optical alternatives) involve screened cables that are normally grounded at both ends. With a good ‘paper plan’, you can see if the system as a whole is earthed, as well as anticipate likely ground loops and any unbalanced/balanced connection issues.
If fault‑finding an existing system, I start by disconnecting absolutely everything apart from the computer, interface, powered monitors and monitor controller (if there is one). I then play some reference material to set a sensible listening volume and check there are no hums of buzzes. If this minimal rig is noisy and involves Class I devices I’d try an isolation transformer between the interface and monitors. If it’s all Class II, I’d try an earthing plug.
Once this core system is quiet, I add the other equipment on the plan, piece by piece, checking again at every stage and correcting any problem introduced by that device using the techniques described above. With good equipment and balanced connections there probably won’t be any problems at all, but by building the system up slowly, testing devices and connections one by one, it’s usually straightforward to find and solve any issues. In contrast, diving into a complex, fully wired system that hums or buzzes can be a confusing and frustrating nightmare.
Ground‑loop problems will always be worse with unbalanced Class I equipment, so try and plug the mains cables from those devices into the same plug board powering the computer/interface/mixer to minimise the loop area. Well‑designed equipment with balanced connections can be plugged into more distant sockets as they won’t mind circulating ground‑loop currents!
Remember, nobody designs their equipment to hum or buzz, and there’s usually a way of connecting them to be completely noise‑free. It just talks patience, logical thinking and educated experimentation. Good luck!
Terminology
The terms ‘earthing’ and ‘grounding’ are often used interchangeably, which can lead to confusion. In this article, I’m generally using ‘ground’ to refer to the electronic circuitry’s ‘zero Volt’ reference and ‘earth’ when discussing a safety earth connection — the green and yellow striped wire in the mains cable which ‘bonds’ the equipment’s metallic chassis to the incoming mains supply’s ‘protective earth’ (PE). The protective earth connection is essential to the safety of some types of equipment (see the ‘Classy Equipment’ box) and ensures that, in the event of a serious internal fault, the mains power to that unit is disconnected promptly by a fuse or breaker. Regulations vary in different countries, but most require automatic ‘breakers’ to switch off the mains power supply if the current draw is excessive and/or if the currents on the Line and Neutral feeds are dissimilar — implying current is being diverted to ground somewhere (possibly via a human!). These automatic breakers can be fuses but are more often resettable mechanical switches known by initials such as RCBO, RCD, RCCB or GFCI.
Classy Equipment
Traditional devices with internal mains power supplies are built into a metal chassis connected to the protective earth via the mains cable. Products built this way are called Class I devices, and include most desktop computers, power amplifiers, large mixing consoles, professional tape recorders, vintage outboard equipment, and so on. They can be usually identified by an ‘earthed’ symbol on the identification plate near the mains inlet.
The electrical safety of a Class I product relies on two things: insulation around the live conductors, and exposed conductive parts being connected to a protective earth. If the insulation breaks down AND the live conductor makes contact with exposed metalwork, a very large current flows directly from the Line (Live) connection to the protective earth, instantly activating legally‑required protection devices within the mains supply (fuse, RCBO, RCD, RCCB, GFCI etc).
Class III devices are powered (or charged) via an external low‑voltage mains adaptor (‘wall‑warts’ and ‘line lumps’), such as laptops, some effects units, keyboards and so on — anything with a low‑voltage power inlet, basically. However, the salient point about these devices is that their mains power units and chargers are always Class II or Class IIFE, so we can consider them as being part of that category when resolving grounding issues.
How To Wire XLRs
XLRs are commonly employed for balanced audio connections, with the audio signal normally passed over pins 2 (hot) and 3 (cold). Of more interest in the context of this article is the cable shield, which is wired to pin 1 (except in one‑end‑only cables where it is isolated at the destination end). Some commercial cables link pin 1 to the connector shell. While this makes no difference with modern equipment, it can cause issues in badly designed equipment since it joins the chassis (via the shell) to the audio reference ground (via pin 1), potentially creating a ground loop. So, as a rule — and especially if working with legacy or poorly designed equipment — it’s best not to link the shell to pin 1. Some argue this omission impacts RF screening at the connection if two XLR cables are joined together (since their shells are floating). While that is technically true, leaving the shells floating avoids the potential risk if they touch some other conductive surface and pick up hostile ground currents! If RF screening is a concern and XLR cables are routinely linked together, consider fitting Neutrik EMC‑series XLR connectors (see below) instead of standard XLRs.
However, in some situations linking the shell to pin 1 can be very helpful, such as when using some vintage capacitor microphones. There was far less RF floating around in the ’50s and ’60s than there is today, and mics from that era often lack the RFI protection that modern designs include as standard. In some, the microphone’s metal case is connected to the XLR pin 1 via a short wire, which, at radio frequencies, has significant inductance greatly reducing the effectiveness of the Faraday Cage screening. By linking the cable shield to the connector shell (and thus directly to the mic’s case), the shielding can be improved dramatically and RFI greatly reduced.
A better technical solution might be to link pin 1 to the shell in the cable XLR via a small capacitor, which would ensure effective grounding at RF, while also preventing ground loops between pin 1 and the case/chassis. Better still, Neutrik’s EMC‑series range of XLRs incorporate a ring of SMD capacitors linking the shell to pin 1 to significantly enhance its RFI screening properties. Although these are more expensive than standard XLRs, they are a very good solution where RF is expected to be a problem.