Via Scoop.it - Equipment and Techniques for Webcasters and Podcasters

This post will only briefly touch on the complex subject of ground loops. The short story is that when you connect a mixer to a computer to a sound system, there is an excellent chance that you will get a ground loop. A ground loop manifests itself as a high pitched whine superimposed on your audio. They can be hard to diagnose, but they can be simple to solve. Contrary to what you may think, the whine is not coming from the computer or the mixer; it is created by interconnecting them.   The device at the link is from Radio Shack and is called a ground loop isolator. It’s really nothing more than a pair of audio transformers. What’s good about these units is that, unlike a lot of Radio Shack merchandise, they are good quality. Transformers can be very expensive, as in a hundred dollars or more per channel. It’s amazing how good these are for about $18US.   Assuming you’re using a mixer, the simplest way to diagnose a ground loop is to monitor the sound with headphones while you can clearly hear the whine. Start unplugging the audio connections to the computers and amplifiers until the whine disappears. In brief, if you disconnect the audio to and from your computer and the whine goes away, you need a ground loop isolator between your mixer and your computer. In this case, if you’re recording and playing computer audio in stereo, you’ll need two of these Radio Shack units.    The reason you have to have two units is that the ground loop is created when the GROUND of the mixer is connected to the GROUND of the computer. Since the ground on the input is the same as the ground on the output, connecting either one will cause the problem. Unfortunately, you’re going to have to do some trial and error.    The Radio Shack ground loop isolators are in stock in most stores. However, if you have some time and want to save some money, check out this eBay seller: http://goo.gl/KECVH The isolators are surplus, are sticky, and have to be cleaned with lighter fluid, but they work great for podcasting.    If you’re having a ground loop problem, you can contact me by email at podcasting at mikephillips.me. I’ll try to help you solve your problem. All I ask in return is that you follow me on Twitter (@mcphillips) and that you tell others about this site.        
Via radioshack.com