Reduces high frequency hiss noise by 20 decibels. Dolby NR (Noise Reduction) is an encode/decode process used when tapes are recorded and played back. Soft, low-level passages are the most perceptible to noise introduction in the audiotape medium. Recognizing this, Dolby NR raises the level of fairly quiet, soft passages in order to make them less prone to noise. When the tape is played back, the level or volume of those areas is reduced back to its normal level so that noise is reduced and the signal still remains the same when played back.