My page about GarageBand is 4 years old — I haven't updated it since the first release of the program back in 2004. Most of it concerned performance issues on slow G3 and G4 systems. If that interests you, go to the old GarageBand page

Why Does My Guitar Cord Make Noise When It Is Not Plugged Into the Guitar?

This is one of the "mysteries" of electric guitars — if you leave your guitar cord plugged into your amp, with no guitar at the other end, the cord itself makes noise when you do simple things with it, like tapping the wire against the floor. The entire cord acts like a microphone. You can even coil it up, hold the coiled cord against your throat and speak or sing, and another person can hear your (muffled) voice coming out of the amp. This "mystery" is really no mystery to electronics engineers. The cord has a voltage bias across it (because the guitar is a very high-impedence current source, like a microphone) and when you tap the cord, small vibrations occur between the sheath (ring, ground) and the signal wire (tip). These vibrations cause changes in the cord's lumped capacitance, which allows small amounts of current to be generated and picked up by the amp.

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© 1996-2008 Robert P. Munafo. Email the author

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