Guitar Buzz

[vlantis]

When I plug in my Acoustic guitar directly into my computer and try to play it in Live I sometimes hear a really high buzzing. What's confusing is that it doesn't always happen. In order for it stop, I have to sit on the floor and touch the metal part of the patchcord with my unclothed foot. Any idea's why this only occurs sometimes and what I can do to keep it from occurring (besides buying a patch board)?

[gomi]

When I plug in my Acoustic guitar directly into my computer and try to play it in Live I sometimes hear a really high buzzing. What's confusing is that it doesn't always happen. In order for it stop, I have to sit on the floor and touch the metal part of the patchcord with my unclothed foot. Any idea's why this only occurs sometimes and what I can do to keep it from occurring (besides buying a patch board)?

it's a ground loop and it has nothing to do with the software.

you want something with a balanced input (ie not the mini headphone
sized input on your computer)

http://en.wikipedia.org/wiki/Tip_ring_sleeve

[Synthbuilder]

When I plug in my Acoustic guitar directly into my computer and try to play it in Live I sometimes hear a really high buzzing.

The guitar is picking up stray electro-magnetic fields. They are all around us, but they will be stronger the nearer you get to the source of them. CRTs, computers and amplifiers, indeed anything with a mains plug, will generate them.

It is probably not an earth loop because to get a loop you need at least two ground wires going back to the guitar and/or analogue input. So using a balanced connection will not help.

The problem is not easily rectified I'm afraid to say. Better quality guitars will have internal screening to prevent this. Electric guitars tend to do better because they have metal strings and your playing action means that your fingers are in contact with the strings. The strings are earthed via the cable so by touching them you too will be earthed. Your body then effectively becomes a screen blocking the unwanted hum fields.

This is what you are doing when you touch the casing of the plugs. You are screening the guitar from these fields.

So I would recommend three things:

Make sure you are well away from anything else electrical. That includes the computer and/or its power supply. You can walk around your room and see where it is quietest.

Use a good quality guitar lead. Its doesn't have to be expensive.

Use ordinary tungsten bulbs and not compact fluorescent bulbs or tubes to light your studio.

One other thing, make sure your computer is actually earthed properly if its mains powered.