Active noise reduction is achieved by a process which amounts to cancellation of the noise by generating an identical sound signal but exactly reversed in phase to the offending noise. A microphone in the ear cup senses the noise (predominantly composed of low frequencies below 300 Hz), develops a signal which is fed to a circuit where it is inverted in phase, amplified, and then drives an earphone creating an anti-noise signal which cancels the intruding noise.
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