Background noise

The combined sounds of transport, industrial, and recreational activities.

A high frequency noise present on analog magnetic tape recordings caused by the size of the magnetic particles used to make the tape.

A crackling or hissing noise caused by electrical interference.

A low, continuous tone caused by electromagnetic interference from the alternating current of the mains electricity. The fundamental frequency of this sound is usually 50 Hz or 60 Hz, depending on the local power-line frequency.

A sound that has been modified in a nonlinear fashion, usually in electronic equipment, to introduce sound correlated with the original signal. In many cases, notably with amplified electric musical instruments, distortion is introduced as an effect by increasing the gain and clipping the source signal.

The audible feedback on a telecommunications channel that allows the speaker to know that the channel is operational.