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Auto Dolby<p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;"><i>The Dolby noise reduction system was invented to reduce tape noise in professional systems and called the 'Dolby A' system.</i></p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">A later system to reduce noise in domestic cassette recorders was known as 'Dolby B'. Later, to improve performance in cassette recorders, the improved Dolby C noise reduction system was introduced. For cassette recorders it meant that a tape could be recorded either without noise reduction: with either Dolby B or Dolby C noise reduction systems.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">For the consumer it meant that the noise reduction system used during recording needed to be noted in some way for later playback, utilising the same noise reduction system. However, if a tape was recorded with two different noise reduction systems on different parts of the tape, identification became even more complex for replay.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">To make things easier for the user, Bang & Olufsen developed and introduced a system to automatically set the noise reduction type on replay, without any user intervention. The system was named 'Auto Dolby'. Any tape recorded on a recorder equipped with the Auto Dolby system would playback correctly on any other recorder with Auto Dolby system, even if the tape contained recordings using different noise reduction on different parts of the tape.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">The system worked by superimposing subsonic tones within the signal to be recorded, with different tones used for Dolby C and for Dolby B. Being subsonic, these tones had no influence on the recorded signal during playback. However, the electronics built into the Auto Dolby circuit detected these signals and switched to the correct noise reduction setting. If no noise reduction was used, no tones were recorded and no noise reduction circuit was set on playback.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">This simple system relieved the user from the chore of noting the noise reduction system used for each recording and switching to the correct system during playback, or alternatively, of listening to the recording using an incorrect noise reduction setting.</p><div><br></div> | Technology | |||
Dolby HX-Pro<p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">When tape recording was in its infancy, the signal to be recorded was fed directly to the recording amplifiers and then on to tape. But it was soon discovered that distortion could be reduced by adding a 'bias' to the signal - at first in the form of a DC signal added to the signal to be recorded and then later a high frequency AC signal. The frequency of the bias signal is always substantially higher than the highest frequency to be recorded and thus does not interfere with the audible signal.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">It was also found that the level of the bias signal is critical to the recording of high frequencies and therefore to the frequency response of the recording. Traditionally, the bias signal level was set at the factory before the tape deck is shipped and remained fixed in use. The level chosen is a compromise for different kinds of music in the judgement of the manufacturer and is different for each brand; and often different for each model within a single brand. The optimum bias level had been the subject of debate between experts for a long time.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">Engineers at Dolby Laboratories suspected that the high frequency content of the music itself had an influence on the frequency response of the recording and launched a system called HX (headroom extension). This was a complex feed forward system that measured the frequency content of the music, calculated the bias required and added this level of bias to the input signal. While the system functioned better than a fixed bias system, it was not the optimal solution.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">Jørgen Selmer Jensen of Bang & Olufsen also had his suspicions about the nature of the bias and its influence on frequency response. But he took a different approach to correcting the problem and in the process got a bonus in performance. He deduced that the high frequencies of the music being recorded were in fact acting as additional bias for the music itself and thus degrading performance. Experimenting with various kinds of music, he devised an algorithm for the bias equivalent added by the high frequency content of the input signal. It was then a relatively simple matter to construct a feedback system that reduced the bias by precisely this amount, on a real time basis. This had the effect of making the frequency response of the recorder linear, once the static bias had been set in the factory, irrespective of the kind of music being recorded.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">The system was found to give an added bonus in use. The undistorted signal level that can be recorded on tape is also dependant on the level of the bias mixed with the audio signal, and was also a part of the factory setting compromise. With HX-Pro it was found that a very much higher level could be recorded, with low levels of distortion. In fact even when the tape was overloaded, the rise in distortion was small compared to recorders with a fixed bias level.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">This system was launched with a license to Dolby Laboratories, who would market the system as Dolby HX-Pro, and has been used for many years not only in cassette recorders, but also in the professional recorder field.</p><div><br></div> | Technology | |||
Dolby Noise Reduction<h2 style="font-size: 18px; line-height: 1.375em; margin: 0px 0px 15px; color: rgb(51, 133, 173); font-family: Arial, Verdana, Helvetica, sans-serif;">Dolby Noise Reduction: A brief history of the Compact Cassette</h2><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;"><i>When the cassette tape was first introduced in the early 1960s it did not pretend to be a high-quality format. It was actually developed as a convenient format for voice recording, especially for secretarial work</i>.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">In 1970, the arrival of noise reduction for cassettes changed the course of the medium. Dolby B-type both reduced tape hiss significantly and spurred many basic improvements in cassette transports, electronics and tape formulations. Soon the cassette was sounding as good as the LP records of the day and it went on to become an extremely popular and widespread medium for recorded music — one which, even today, continues to provide an unmatched combination of affordable costs, portability, playback versatility and recording capability.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">As listeners' expectations for high-quality playback grew, various improvements on the original Dolby B-type system arose to the challenge. Dolby C-type and S-type noise reduction systems apply the same principles to even more dramatically reduce tape hiss and enhancements like Dolby HX Pro headroom extension improve the quality still further.</p><h2 style="font-size: 18px; line-height: 1.375em; margin: 0px 0px 15px; color: rgb(51, 133, 173); font-family: Arial, Verdana, Helvetica, sans-serif;">Dolby B-type Noise Reduction</h2><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">Dolby B-type noise reduction is the original Dolby system designed for consumer tape recorders. It is included in all but the least expensive cassette machines today and is used in the preparation of the vast majority of pre-recorded cassettes. It is also incorporated in many stereo VHS videocassette recorded to improve their (mono) linear audio tracks and, in a modified form, in Dolby Surround decoders. Dolby B-type provides 10 dB of noise reduction at the higher frequencies where tape hiss predominates.</p><h2 style="font-size: 18px; line-height: 1.375em; margin: 0px 0px 15px; color: rgb(51, 133, 173); font-family: Arial, Verdana, Helvetica, sans-serif;">Dolby C-type Noise Reduction</h2><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">Dolby C-type noise reduction was developed to improve the cassette medium still further by providing twice the tape hiss reduction (20 dB) of Dolby B-type. It is offered along with Dolby B-type in a variety of mid-range and premium cassette decks and players. Dolby C-type is also used in many professional VCRs.</p><h2 style="font-size: 18px; line-height: 1.375em; margin: 0px 0px 15px; color: rgb(51, 133, 173); font-family: Arial, Verdana, Helvetica, sans-serif;">Dolby S-type Noise Reduction</h2><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">Introduced in 1990, Dolby S-type is based upon the principles of the professional Dolby SR (Spectral Recording) process. It not only provides still more tape hiss reduction (24 dB), but also reduces low-frequency noise by 10 dB. Thus, it permits recording high-level signals at the frequency extremes more accurately and cleanly. In listening tests it compares very favourably with CD recordings, with most listeners judging the quality of Dolby S-type encoded tapes as comparable with or in some cases superior to the playback quality of the CD. Dolby S-type is still steadily gaining momentum and is being incorporated first in state-of-the-art decks for the most discerning listeners.</p><h2 style="font-size: 18px; line-height: 1.375em; margin: 0px 0px 15px; color: rgb(51, 133, 173); font-family: Arial, Verdana, Helvetica, sans-serif;">Dolby HX Pro</h2><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">Not a noise reduction system, Dolby HX Pro makes it possible to record loud musical passages with fewer high-frequency losses and less distortion. It is available in better cassette decks and is also widely used by the recording industry to improve the quality of pre-recorded cassettes through its process of reducing the effects of tape saturation. As no encoding of the signal takes place, no playback decoding circuitry is required to realize the benefits of Dolby HX Pro.</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">Dolby Headphone Stereo is a new, powerful, digital signal processing system that was developed in 2002 to recreate the sound from each audio channel as if it were being played back from a speaker placed in an acoustically-designed room. In effect, Dolby Headphone Stereo creates virtual loudspeakers in a virtual room. The result is much more dynamic, listening experience: a more natural way of listening to music. Dolby Headphone has the technology to offer three impressive 'Listening rooms' which are controlled from the main unit or the in-line remote control they offer. These are:</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;"><strong>The Studio</strong>: replicates the music played in a small acoustically-damped room, giving perfect sound</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;"><strong>Live</strong>: recreates a more open live sound as if you were listening to your favourite band on tour</p><p style="line-height: 1.5em; margin: 0px 0px 20px; color: rgb(83, 101, 124); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;"><strong>Dome</strong>: gives the impression of hearing music in a Large concert hall. Without having to be there</p><div><br></div> | Technology |