While some loops -such as that sample you found once that inspired a whole track, or Basic Channel’s Q Loop– can be great, ground loops can be the bane of many a studio. Can there be many things more frustrating than getting all your new and shiny hi-tech pro-audio gear unpacked and installed, putting aside an afternoon for a recording session, powering up and being greeted by a perpetual hum from your monitor speakers? Nope. Probably not…
So, what’s making that noise and what can you do about it? We’ll keep this simple (mostly because it’s Friday afternoon and I don’t really have the intellectual capacity for this at the best of times), but try and cover the basics of what it is and how to deal with it.
Ground loop madness!
First thing first, what is making that hum? If you imagine an unbalanced cable, such as an RCA phono type cable, there is a core and a screen. The screen is earthed, and so should be a stable 0 Volts, the audio signal is, in effect, the difference in voltage between that 0 Volt screen and the core. But what if that screen doesn’t quite stay at 0 Volts all the time? Let’s read on…
Thanks to the wonderful world of Ohm’s law (Voltage = Current x Resistance or V=IR), which demonstrates -with a wonderful, simplistic beauty- how current and resistance affect voltage we can see that, if a current flows in the screen, there will be a change in voltage in the screen away from our 0 Volts. So, if you aren’t sending an audio signal, the core of the cable will be at 0 Volts, your screen won’t be, so you hear a noise.
Whence comes my ground loop screen current?
One reason is that ground isn’t always the same. For example, imagine you have two pieces of gear connected by an audio cable, but powered by being plugged into two different power outlets. Your computer and audio interface for example. Strange as it may seem, the earth potential from outlet to outlet can sometimes be different. As your two pieces of gear are connected, the changes in earth potential mean that there is a voltage difference between the pieces of gear, causing a current to flow in the screen.
In more complicated studio setups with more pieces of equipment and more cables, you can end up inadvertently creating a ‘loop antenna’. If you create a ‘circle’ of wiring, this can act as an antenna, which can pick up all sorts of signals, from radio transmissions to the broadcasts of alien races trying to communicate, but also your mains power. So, if you’re in the UK, expect a hum at 50 Hz, 100 Hz, 150 Hz…
Fixing that ground loop!
Obviously, there are lots of ways of making buzzy loops in your studio, but you can’t be expected to work under such conditions, so what is to be done about it? Abbey Road probably doesn’t have to deal with them, so there must be an answer…
One of the first things to try is to plug all your equipment into the same outlet using a power strip. Make sure and total up the current draw of your equipment so that you don’t exceed the rated maximum. This should ensure that all your gear is now earthed at the same potential.
Where possible, connect your studio together using balanced connections rather than unbalanced connections. Balanced connections use an extra conductor to reject these buzzes and can help keep your studio quiet.
You can always try to track down the cause of the problem by systematically unplugging pieces of equipment and see when the hum goes, then you can try and work out how to deal with it!
If you use a laptop, try unplugging it and running on the battery. Laptop power supplies have quite a reputation for being buzzy! You can always keep it plugged in for the majority of your work and just run from the battery when you’re recording with a microphone or doing some critical mixdowns.
A power conditioner may not fix your buzz and hum problems, but can improve matters in some circumstances. However, given your investment in your studio equipment, giving them nice, filtered power is a worthwhile thing to do, and many power conditioners include surge protection as well, which is a sensible thing to have in front of all your pro audio equipment!
A DI box is a very handy thing to have. By using a transformer in the signal path, there is now no direct electrical signal path from the input to the output and can therefore be a great way of eliminating ground loops. Many also have a ground lift switch to uncouple the audio earth from the electrical earth.
What you must never, ever do -ever- is remove the electrical earth from any of your equipment, power supplies or plugs. That would be a very, very silly thing to do.
While all of this talk of getting rid of noise in studio should hopefully benefit most producers, maybe we’re being too hasty, could it be music? Moomba2-step-humcore anyone…?
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