A wide range of solutions to this annoying, frequent problem that happens in the studio and on the stage. Plus, a discussion of power issues, including a sidebar by noted audio consultant Jim Brown.
You’re recording an electric guitar, or amplifying it through a P.A., and there it is: hum! This annoying sound is a common occurrence.
Acoustic guitars fitted with pickups can have the same problem.
Hum is an unwanted 60 Hz tone—50 Hz outside the U.S.—plus harmonics. If the harmonics are especially strong, the hum becomes an edgy buzz.
Let’s take a look at what’s going on and how to fix it. First we need to review how an electric guitar works.
Inside The Electric Guitar
Built into the guitar, under the strings, is a magnetic pickup: a transducer that converts the strings’ vibration into an electrical signal. The pickup is a bar magnet wrapped with thousands of turns of wire, forming a coil.
When the player plucks the steel strings, they vibrate next to the magnet, producing a similar vibration in the magnet’s magnetic field, which in turn causes a varying current in the coil.
Another type of pickup uses a separate magnet under each string. Some pickups have a screw on each magnet’s polepiece to adjust the distance between the polepiece and string, allowing level control of each string.
A humbucking pickup uses two coils wired in series but with opposite polarity so that they cancel common hum fields. One coil is mounted far from the strings. [read]