You're just a big ole' Bucket O' Noise

"So, why does the noise get quieter (or, sometimes, louder) when I touch the strings?

I've been answering that question for many years and as often as not it seems like a lot of folks just didn't get it.  I think I've finally figured out why.  Most folks seem to be looking at the situation backwards.  They say things like, "well, when I ground the strings by touching them..."  Except in some extremely rare circumstances the human body makes a lousy ground for noise.  In fact, it is almost always more accurate to consider the human body a big bucket of noise!  Very rarely is a person effectively grounded (how often do you play standing barefoot on a metal plate or with one hand wrapped around a water pipe?), and even when part of them is grounded internal and skin resistance will separate other parts of their body from ground.

You may be grounded well enough to be electrocuted by high voltage and still remain a noise source, instead of a ground for noise!  Ohms law tells us that the current through a conductor is related to the resistance of the conductor and the voltage applied.  It only takes a few milliamps to stop the heart, and it takes about 100 volts to push that much current through the middle of your body in most circumstances.  So, a person's resistance may be low enough and they may be grounded well enough that a high voltage can push a lethal current through them while they remain a source of noise.

The noise (usually) gets quieter when a person touches their guitar strings because the strings are grounding the player!  Almost all guitars have a wire that connects the bridge (or tremelo claw) to the ground terminal of the output jack so that the strings are gounded.  When someone picks up the guitar and holds it close to them, that person's body is acting as a radiator or reflector of noise in the vicinity, "concentrating" it, if you will, close to the guitar's pickups.&nbps; Then, when they touch the strings their body is suddenly much better grounded, shunting noise to ground.  They go from being a radiator or reflector to being a shield.  How much the noise is reduced depends on the person's internal and skin resistance – a person with high resistance may still be concentrating a bit of noise around the pickups while a person of low resistance may completely shunt the noise to ground.

If the strings are not grounded, the noise will usually actually get louder when someone touches the strings because the strings act like very good radiators to concentrate the noise from the person's body right over the pickups.  If the player's body was grounding the strings, the noise would get quieter when the player touched the strings, even if there was no bridge ground wire!

Now, I realize that this may be more of a paradigm shift than some folks are able to accept, so here's a little experiment you can run to demonstrate these facts for yourself.  The experiment doesn't require anything but an amplifier and an instrument cord.

1. Plug the instrument cord into the amp.  Make sure that the amp is plugged into a properly wired mains socket.  Turn the amp on and the gain up high.  If it's a tube amp give it a few moments to warm up.
2. Dress as you would normally dress to play and sit or stand where you would normally play (i.e. no sitting bare-nekid on the radiator).
3. Take the free end of the cord in your hands, being careful not to touch the metal plug shell (if it has a metal shell) or the long ground shank of the plug (there is no hazard here, we just don't want to be touching it right now).  Touch just the very tip of the plug lightly with your finger.  Did the noise get louder?  If your body were a ground for noise, the noise would have gotten quieter!
4. Now move your finger so that it is lightly touching both the tip and the ground shank of the plug.  The noise level should change – how much it changes is a function of your skin resistance.  For most people the noise level will drop but will still be louder than when they weren't touching the tip at all.
5. Now, wrap your hand tightly around the plug so as much of your bare skin is in contact with both the tip and ground as possible.  The noise level should drop some.  Again, how much it drops is a function of skin resistance.
6. Lastly, if you are near your computer monitor or a television, touch just the tip of the plug again then reach over with your other hand and lay the palm flat against the screen of the monitor (while it's on).  The noise should get much louder as your hand approaches the monitor face.  This is demonstrating that your body is "channeling" noise.

Once one realizes that they are not grounding the strings when they touch them, one can begin to understand the noise problem better.  Now one can see why the noise getting louder as one touches the strings is indicative of either a missing or broken string ground wire or of the wires to the output jack being reversed.  (With reversed output wires, touching the strings is exactly like touching the tip of the plug in the experiment above.)