Between the two limits, a varying level of pre-emphasis is applied. For instance, in Dolby B, a low-level signal will be boosted by 10 dB, while signals at the "Dolby Level", +3 VU, receive no signal modification at all. Within each band, the amount of pre-emphasis applied depends on the original signal volume. The differences in the various Dolby products are largely evident in the precise set of frequencies that they use and the amount of modification of the original signal volume that is applied to each of the frequency bands. It is the lower-frequency sounds that are often loud, like drum beats, so by only applying the companding to certain frequencies, the total amount of distortion of the original signal can be reduced and focused only on the problematic frequencies. This takes into account the fact that tape noise is largely heard at frequencies above 1,000 Hz. On top of this basic concept, Dolby noise reduction systems add another improvement. This basic concept, increasing the volume to overwhelm inherent noise, is known as pre-emphasis, and is found in a number of products. When the volume is reduced on playback, the noise level is reduced by the same amount. The idea is to increase the volume of the recording only when the original material is not already loud, and then reduce the volume by the same amount on playback so that the signal returns to the original volume levels. One cannot simply increase the volume of the recording to achieve this end tapes have a maximum volume they can record, so already-loud sounds will become distorted. If the recording level is adjusted so that the music is always loud, then the low-level noise would not be audible. When the music is loud, the low background hiss level is not noticeable, but when the music is soft or in silence, most or all of what can be heard is the noise. The signal-to-noise ratio is simply how large the music signal is compared to the low level of tape noise with no signal.
#PLAYBACK PRO SYSTEM PLUS#
Noise and frequency response analysis of a Nakamichi 580M high-performance cassette deck with Dolby B-type noise reduction systemĭolby noise reduction is a form of dynamic pre-emphasis employed during recording, plus a form of dynamic de-emphasis used during playback, that work in tandem to improve the signal-to-noise ratio. Aside from Dolby HX, all the Dolby variants work by companding: compressing the dynamic range of the sound during recording, and expanding it during playback. Dolby B, C, and S were designed for the consumer market.
#PLAYBACK PRO SYSTEM PROFESSIONAL#
Of the noise reduction systems, Dolby A and Dolby SR were developed for professional use. It is common on high fidelity stereo tape players and recorders to the present day. The first was Dolby A, a professional broadband noise reduction system for recording studios in 1965, but the best-known is Dolby B (introduced in 1968), a sliding band system for the consumer market, which helped make high fidelity practical on cassette tapes, which used a relatively noisy tape size and speed.
#PLAYBACK PRO SYSTEM SERIES#
A Dolby 361 A-type noise reduction module Dolby noise-reduction system Product typeĪ Dolby noise-reduction system, or Dolby NR, is one of a series of noise reduction systems developed by Dolby Laboratories for use in analog audio tape recording.
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