Dealing With Laptop Noise and Ground Loop Interference
If you have nasty data type noise coming from your laptop's audio interface then it's probably a ground loop - let's sort that out
We often hear reports of weird noises coming from the audio interfaces when attached to a laptop. Sounds a lot like electrical interference, mixed with scratchy data type noises and combined with mechanical noises triggered from hard disks or mouse movement. The sort of noise can vary but the cure is always the same – pull the power out of the laptop and the noise goes away. Laptop battery life is not all that great so running on batteries is not an ideal solution. So what’s causing this issue and how do we cure it?
Ultimately it’s an earth loop. Earth (or “ground”) problems are usually associated with some kind of hum or low level noise but that is what’s happening here – which is why it goes away when you disconnect the power and consequently the earth.
Here's a video we made highlighting the problem and some of the solutions mentioned below:
A ground loop is created when there is more than one earth path between two bits of equipment. When the two items are plugged in the earth’s are essentially joined and create a looped circuit along which a current can flow. Audio cables are grounded through the shielding mesh that goes around the outside and that’s what allows the earth interference to get added to the audio signal.
With regular audio gear this loop of wire can pick up the 50Hz mains power and you hear the low rumbling hum. With laptops the loop of wire is surrounded by complex electronics all shifting current about the place and generating magnetic fields as they go. As the fields cross the earth loop a current is induced and it arrives on the audio cable as weird, electrical, data noise. Let’s break that down a little:
Current runs through circuits
Current creates a magnetic field
The earth loop of power cables audio cable shielding sits in that field
The current is transferred to the earth loop by induction.
Appears in the audio signal as noise
So what can be done? Well the obvious answer is that you need to kill that earth loop – needs to be broken somehow somewhere. Now before you start snapping the earth pin off your plug please be aware that they are there for a reason and provide an escape route for mains voltage should a power fault occur. It’s dangerous, don’t do it. Here’s some better solutions:
Get a laptop power supply that has a double-insulated two pin (and therefore no earth pin) power connection. These power adapters don’t require the earth and are completely safe in the event of a fault due to that insulation. When you buy one make sure it will support the correct voltage your laptop needs and has a suitable connector that will fit your laptops power socket. We’ve used PowerCool Universal adapters with Livebooks with great success and they are available all over the place – google and you’ll find them.
Get a hum eliminator or “ground lift” DI box. This goes in the audio signal chain, usually between your audio interface and the mixer or speakers. It simply breaks the grounding in a safe way and all the noise vanishes. There are various makes but we’ve used the Behringer HD400 which works perfectly. DI boxes that include a ground lift can also serve this purpose.
Balanced cables – if you are using balanced cabling all the way down the audio signal chain then you shouldn’t encounter this problem. If you have balanced connections at either end then make sure your cables are correct and off you go.
Pseudo balanced cables – The old school method is to make up your own cables and sprinkle them with some engineering wizardry. I’d not encountered this before so I’ll let chief Wizard Martin Walker from a November 2004 article in Sound On Sound magazine explain: You just buy twin-core screened (mic) cable instead of single-core screened, and then solder an unbalanced TS plug on one end (the soundcard end) and a balanced TRS jack one to the other (the mixer end). The 'tip' connections are made as normal using one cable core, while the 'sleeve' of the unbalanced end is connected to the 'ring' connection at the balanced end using the other cable core, and the 'sleeve' of the balanced end is either left unconnected, or preferably connected via a series eighth-Watt metal-oxide resistor of between 50(omega) and 500(omega) (I normally use 100(omega)) to the 'sleeve' connector at the unbalanced end. Such an approach will completely cure most soundcard ground-loop problems, and if you're going to solder up your own leads anyway it will only cost you a few pence more.
On balance getting a double-insulated power adapter is probably the best solution, although to be on the safe side, particularly if you take your laptop gigging and you’ve no idea what you’ll be plugging into, it’s useful to have a hum eliminator in your bag.