Dolby noise reduction system

Dolby NR is a noise reduction system developed by Dolby Laboratories for use in analogue magnetic tape recording. It works by companding, i.e. reducing the dynamic range of the sound during recording and expanding it during playback. It is not the only system that works in this way, but it is the most widely used.

Related Topics:
Noise reduction - Dolby Laboratories - Magnetic tape - Companding

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Several types of Dolby NR were developed, including A (1966), B (1968), C (1980), S, and SR. Dolby A type is a multiband professional system. Most widely used in consumer products is the B type, which allows for acceptable playback on devices without noise reduction. Most pre-recorded cassettes use this variant. In the mid-1970s, some expected Dolby NR to become normal in FM radio broadcasts and some tuners and amplifiers were manufactured with decoding circuitry.

Related Topics:
1966 - 1968 - 1980 - Cassette - FM radio

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The Dolby systems are designed specifically with either professional or consumer users in mind—Dolby A and Dolby SR were developed for professional use. Dolby A operates in four bands providing 10 dB noise reduction across the full frequency spectrum. Dolby B, C, and S were designed for the consumer market. Dolby B was developed as a single band system providing up to 10 dB noise reduction on frequencies above 1 kHz. It was less expensive to implement but provided less effective noise reduction. Dolby C provides up to 20 dB noise reduction in the high frequency range.

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Dolby developed another system in 1982 called Dolby HX, which works by modifying the ultrasonic bias signal, used by all analogue tape decks, to increase the headroom for high-frequency audio signals. HX stands for "headroom extension". This system was modified by Bang & Olufsen and marketed by Dolby as Dolby HX Pro. (Reference.) While not a noise reduction system per se, Dolby HX Pro provides a cleaner original recording.

Related Topics:
1982 - Bias signal - Bang & Olufsen

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Dolby's analogue noise reduction systems, though still used in some professional applications, have been made obsolete by the widespread adoption of digital audio (in the form of compact discs, MP3s, MiniDiscs, and to a lesser extent DAT) in the home for entertainment and recording.

Related Topics:
Digital audio - Compact disc - MP3 - MiniDisc - DAT

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