Tutorial: Fixing a Noisy Line, Part 1

Something I’ve been combating lately in my recording is line and interface noise. As I mentioned recently, the Lightsnake USB interface I’ve been using worked OK with my acoustic, but once I started recording with an electric guitar, the noise is much more prominent. There are 2 ways to correct a noisy interface: 1) Buy Better Gear, or 2) Use the tools you have to try to minimize the audible noise coming through.

Since we are about frugality, we will assume that you don’t have the scratch right now to pick up a better interface. (I’m crossing my fingers and hoping a better interface box is under the Christmas tree, or at least some cash to buy it guilt-free.) That leaves us with the duct tape and chewing gum solution (i.e. a non-ideal solution) to cleaning up your audio.

Check Your Wires
The first thing to check when you’ve got excess noise coming on your input is to check the connections. Do you get pops and crackles when you touch the cables while connected? You might have a broken wire that is adding noise when it is flexed. It might be cracked shielding in the cable that might be picking up interference. Try to eliminate as many sources of noise. And remember, an incoming audio source MUST be plugged in to something when you’re testing. A cable end dangling on the floor usually will pick up a little charge from the air, perhaps a little extra hum from finger grime on the plug ends. Also, make sure the volume on the instrument is turned all the way down. This will help you isolate whether it is the instrument’s electronics causing the noise or something with the line/interface itself. If you identify a possible broken wire, try to swap it out and see if that helps.

Check Your Gear
If you have a clean line when the instrument’s volume is turned off, then you might have a problem in your gear itself, or interference causing problems with the gear. I have found that CRT monitors will cause a little extra hum on some lines. If you can, turn off the CRT and see if the sound goes away. If this is the case, then see if you can re-route things to keep the lines further from the monitor.

Another source can be some fluorescent light fixtures. I have used a couple that will generate a lightsaber-style hum on lines nearby. Turn off the lights and see if that helps.

If you can determine that the instrument is somehow at fault, but you can’t identify anything else reacting with it, then you may want to consider borrowing someone else’s similar instrument to see if it exhibits the same problem, or take the instrument to a qualified tech and see if there are modifications you can make to reduce the noise. (For guitars, these usually either means replacing pickups, switches, or at least having the wiring re-soldered to make better connections.)

Extra Hardware
Sometimes you can isolate that it is the instrument, but there’s nothing you can do to directly fix it. There are some line filters and power filters that might be able to help fix your signal. Frankly, most of those are out of my price range, especially for a “it MIGHT fix the problem” potential solution. If you have friends with this type of extra gear, by all means borrow their equipment and see if it cures your ills. If it does, start saving your loose change to buy one for yourself. Again, this falls under the “Buy Better Gear” option, which isn’t always a viable course to take.

It’s the Interface!
In my situation, I was able to isolate it to the Lightsnake itself. As I explained in my post “Eating My Own Words”, it became more evident with the electric guitar than with the acoustic, but it is definitely the interface itself, since I don’t get the same problem with other line or microphone inputs on the same computer.

Software Solutions
If your final verdict is like mine, then the garbage on the input can’t be directly avoided without buying new hardware, so you have to try to clean up the signal after it has been received. In Part 2 of this tutorial, we will look at software solutions to this problem.