Dolby Noise Reduction refers to a family of analog signal processing systems developed by Dolby Labs, designed to decrease the background hiss inherent in magnetic tape recordings. The line includes consumer and semi-professional formats, such as Dolby B, C, and S types, and professional studio formats, such as Dolby A and the advanced Dolby SR. All operate on the compander encode and decode principle, where the signal is processed across multiple frequency bands during recording, boosting the level of quiet and high-pitched sounds to mask noise, and restored to its original state during playback. It is crucial that a tape recorded with one of these systems be played back with the same type of decoding enabled so that the sound does not appear muffled or have its dynamics incorrectly altered.