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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. Noise reduction is the process of removing noise from a signal. ...
The Dolby logo Dolby Laboratories, Incorporated (Dolby Labs) is a company specializing in audio compression and reproduction. ...
Magnetic tape is a non-volatile storage medium consisting of a magnetic coating on a thin plastic strip. ...
A waveform before and after the compression stage of companding In telecommunication, signal processing, and thermodynamics, companding (occasionally called compansion) is a method of reducing the effects of a channel with limited dynamic range. ...
Several types of Dolby NR were developed, including A (1966), B (1968), C (1980), S, and SR. 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. 1966 (MCMLXVI) was a common year starting on Saturday (link goes to calendar) // Events January January 1 - In a coup, Colonel Jean-Bédel Bokassa ousts president David Dacko and takes over the Central African Republic. ...
1968 (MCMLXVIII) was a leap year starting on Monday (the link is to a full 1968 calendar). ...
1980 (MCMLXXX) was a leap year starting on Tuesday. ...
Typical audio Compact Cassette. ...
FM radio is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation to provide high-fidelity broadcast radio sound. ...
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.
The Dolby SR system is a much more aggressive noise reduction approach than Dolby A. It attempts to maximise the recorded signal at all times using a complex series of filters that change according to the input signal. As a result it is the much more expensive to implement than Dolby B or C, but is capable of providing up to 25 dB noise reduction in the high frequency range. Dolby SR is only found on professional recording equipment. [1] [2]
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 much simpler than Dolby A and therefore much less expensive to implement but provided far less effective noise reduction. Also the Dolby B recordings are acceptable when played back on equipment without Dolby B.
Dolby C provides up to 20 dB noise reduction in the high frequency range - but the resulting recordings sound much worse on equipment that does not have Dolby C noise reduction.
Dolby S system is basically a cut down version of Dolby SR and uses many of the same techniques. It is capable of 10 dB of noise reduction at low frequencies and up to 24 dB of noise reduction at high frequencies.[3] Dolby S is found on some Hi-Fi and semi-professional recording equipment. Dolby S is much more resistant to playback problems caused by noise from the tape transport mechanism than Dolby C.
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. 1982 (MCMLXXXII) is a common year starting on Friday of the Gregorian calendar. ...
Tape bias is a high-frequency signal (generally from 40 to 150 kHz) added to the audio signal recorded on an analog tape recorder. ...
Bang & Olufsen (B&O) is a Danish company that designs high end audio products, television sets, and telephones. ...
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. Digital audio refers to audio signals stored in a digital format. ...
It has been suggested that CD Rot be merged into this article or section. ...
MP3 is a popular digital audio encoding and lossy compression format invented and standardized in 1991 by a team of engineers working in the framework of the ISO/IEC MPEG audio committee under the chairmanship of Professor Hans Musmann (University of Hannover - Germany). ...
The Sony MZ1 MiniDisc player, the first to hit the market in 1992. ...
This article needs to be cleaned up to conform to a higher standard of quality. ...
How Dolby B works
Dolby B (and C which is similar) is a form of dynamic preemphasis. The background hiss of a tape (white noise) is unnoticeable if it is masked by a stronger audio signal, especially at higher frequencies. This is called psychoacoustic masking. When the tape is recorded, the amplitude of the signal above 1 kHz is used to determine how much pre-emphasis to apply - a low level signal is boosted by 10dB (Dolby B) or 20dB (Dolby C). As the signal rises in amplitude, less and less pre-emphasis is applied until at the "Dolby level" (+3 VU), no signal modification is performed. On playback, the opposite process is applied (deemphasis), based on the signal level. Thus as the signal level drops, the higher frequencies are progressively more strongly filtered, which also filters the constant background noise level. The two processes cancel out as far as the signal is concerned, so it is reproduced faithfully, but only one process (the de-emphasis) is applied to the noise, which is thereby reduced. In processing electronic audio signals preemphasis refers to a system process designed to increase, within a band of frequencies, the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse...
Four thousandths of a second of white noise White noise (Sample â–¶(?)) is a random signal (or process) with a flat power spectral density. ...
A schematic representation of hearing. ...
Psychoacoustics is the study of subjective human perception of sounds. ...
Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation, that is, magnitude of the maximum disturbance in the medium during one wave cycle. ...
The decibel (dB) is a measure of the ratio between two quantities, and is used in a wide variety of measurements in acoustics, physics and electronics. ...
The calibration of the recording and playback circuitry is important for faithful cancellation of the complementary processes, and is easily upset by poor quality tapes, dirty playback heads or using incorrect bias levels. This usually manifests itself as muffled-sounding playback, or "breathing" of the noise level as the signal varies.
Dolby HXPro HX or "Headroom eXtension" is a method for further increasing the dynamic range of a cassette tape. Because tape is magnetic, it is inherently non-linear in nature, due to the hysteresis of the magnetic particles. If an analogue signal were recorded directly onto magnetic tape, it would be reproduced extremely distorted, due to this non-linearity. To overcome this, a high frequency signal is mixed in with the recorded signal, which "pushes" the envelope of the signal into the linear region. Dynamic range is a term used frequently in numerous fields to describe the ratio between the smallest and largest possible values of a changeable quantity. ...
Hysteresis is a property of systems (usually physical systems) that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state: that is, systems whose states depend on their immediate history. ...
For the Analog Science Fiction and Science Fact publication, see Astounding Magazine. ...
Non-linearity is a slight distortion of a single frequency into multiple frequencies within the human or mammalian auditory system. ...
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