The audible aspect of this sort of electric hum is produced by amplifiers and loudspeakers (note that this is not to be confused with acoustic feedback).
The other major source of hum in audio equipment is shared impedances; when a heavy current is flowing through a conductor (a ground trace) that a small-signal device is also connected to.
Another solution is to connect the source and destination through a 1:1 isolation transformer, called variously audio humbucker or iso coil.
[2] In certain vacuum-tube radio receivers, a winding on the dynamic speaker field coil was connected in series with the power supply to help cancel any residual hum.
Some other common applications of this process are: In musical instruments, hum is usually treated as a nuisance, and various electrical modifications are made to eliminate it.
These demos did not see any official release at the time, nor were they properly recorded for Double Fantasy or its follow-up Milk and Honey, but they did spread as bootlegs amongst Lennon fans.
In the mid-1990s, as part of the Beatles anthology series, the three surviving members, Paul McCartney, George Harrison, and Ringo Starr, regrouped to record initially incidental music for the albums, but decided to rework some John Lennon demos instead.
This, and to a much bigger extent, Harrison's distaste for that particular demo, lead to it being scrapped altogether,[5] although reports circulated in the years since that McCartney was hoping to finish it.
In 2023, the mains hum was finally removed thanks to Peter Jackson's sound source separation technology,[9] and the track was released on November 2, 2023.
Broadcast television frame rates are chosen to match the line frequency, to minimize the disturbance these bars cause to the picture.
A hum bar can be caused by a ground loop in cables carrying analog video signals,[12] poor power supply smoothing, or magnetic interference with the cathode-ray tube.