Buzz, hum, or digital noise after plugging in over USB

If you hear a buzz, a hum, or a harsh digital whine in your headphones as soon as your modeler or interface is connected to the computer by USB, it is almost always a ground loop in your cabling. It is not coming from Fret Beam. The dry signal Fret Beam reads over USB is generated digitally inside your modeler and never touches the analog cables where the noise lives. The noise is in your monitoring and, more importantly, in whatever you are recording.

The setup that causes it

Most teachers using Fret Beam end up with this chain:

• A modeler (Pod Go, Helix, Katana, and so on) connected to the computer by USB, so Fret Beam gets the clean dry signal.
• An audio interface (Focusrite, Audient, and so on) also connected to the computer by USB, for the mic, headphones, and hearing the rest of the computer's audio during a lesson.
• Analog cables from the modeler's outputs into the interface's inputs, so you can hear yourself with no latency.

Both devices are tied to the computer's ground through their USB cables, and tied to each other through the analog cables. That makes a complete ring of ground conductors, and a ring like that picks up noise. Desktop PCs are far worse than laptops here, and front-panel USB ports on a desktop case are the worst of all.

How to confirm it is a ground loop

Try each of these one at a time and listen:

1. Unplug the modeler's USB cable. If the noise stops, it is a ground loop.
2. Plug the USB back in and unplug the analog cables between the modeler and the interface instead. If the noise stops again, that confirms it. Either leg breaks the ring.
3. Power the modeler off but leave its USB connected. If the noise is still there, that is also a ground loop. The powered-off unit is just a passive link in the ring.

If none of those changes the noise, the problem is somewhere else. Check the interface's gain, your mic, and your headphone cable, then write to us.

The fix: use balanced cables into your interface

Run balanced cables from the modeler into the interface. On most gear that means a TRS 1/4" cable or a 1/4" TRS to XLR cable, going into a balanced input on the interface (an XLR or combo jack, or a TRS line input). Check your modeler's manual for which outputs are balanced. A balanced connection does not break the ground ring, but the interface's balanced input rejects the ground noise as common-mode interference. In practice that removes it. The cost is a pair of cables. Do this before buying any isolator or other box.

If your modeler has a ground lift switch on its outputs (the Helix does), use balanced outputs and flip the lift. That handles the problem at the source.

If you still hear it

The steps below each help on their own, and they stack. Try them in order.

1. Move the USB cable to a rear port on the computer. On a desktop, the ports on the back of the case connect straight to the motherboard and are much quieter than the front-panel ports. On a laptop, try each port.
2. Skip the USB hub. Plug the modeler and the interface directly into the computer. If you must use a hub, use a powered one with its own supply.
3. Put everything on the same power strip. The computer, the modeler, the interface, and any powered monitors should share one outlet. Different outlets, especially on different circuits, make the ground difference bigger. This reduces the noise but rarely removes it on its own.
4. Use a short, shielded USB cable. Long or cheap USB cables pick up more noise. Two meters or less, from a known brand.
5. Keep audio cables away from power supplies and wall adapters. Do not run 1/4" cables in a bundle with power cords or lay them on top of a laptop charger.
6. Turn the modeler's output level up and the interface's input gain down. A hotter signal into the interface with less gain on top of it raises your signal above whatever noise remains.
7. Try unplugging any other USB devices one at a time (external drives, lighting, a second interface). One of them may be adding its own noise to the shared ground.

Isolators, only if the above did not work

If balanced cables are not an option, or a hum still remains, an isolator on one leg of the ring will break it:

• A transformer isolator on the analog leg (Ebtech Hum Eliminator or ART DTI class, roughly $50 to $70). It sits between the modeler's outputs and the interface's inputs.
• A high-speed USB isolator on the modeler's USB leg (roughly $150 to $350). Make sure it is USB 2.0 high-speed or better, or the modeler's audio will drop out.

A ground-lift plug adapter on a power cord is not a fix. Do not remove the ground pin from anything.

What this does not affect

The tab Fret Beam writes comes from the digital USB stream, so a noisy analog chain does not change what the app hears or detects. If notes are missing or wrong, that is a separate problem. See Getting your guitar into Fret Beam and Troubleshooting.