wave of the opposite polarity. This method employs the use of an active sound generating device, such as a loudspeaker to counteract ambient noise in an area. See noise-canceling headphone. Workers in noisy environments may favor this method over ear plugs. Noise reduction: In sound and video equipment, noise reduction is the process of removing noise from a signal. This is strictly for electronic noise or noise which has been detected and put into electronic form. Noise canceling: If both the noise and the signal are received by an electronic or digital medium, noise can be filtered from the signal electronically and retransmitted without the noise. See noise-canceling microphone. Helicopter pilots rely on this technology to speak on the radio. See also Acoustic signature Noise reduction, for electronic noise Sound masking, for noise masking by saturation Pink noise Stealth technology, for signature reduction in general Longitudinal wave Soundproofing Mechanical resonance Sound masking Seismic retrofit Helicopter noise reduction Muffler Deperming Degaussing References Acoustics Noise control Stealth technology