dbx: Аналогтық дыбыстың шуын азайту жүйелері

Family of noise reduction systems

dbx is a family of noise reduction systems developed by the company of the same name. The most common implementations are dbx Type I and dbx Type II for analog tape recording and, less commonly, vinyl LPs. A separate implementation, known as dbx TV, is part of the MTS system used to provide stereo sound to North American and certain other TV systems. The company, dbx, Inc., was also involved with Dynamic Noise Reduction (DNR) systems.

The original dbx Type I and Type II systems were based on so called "linear decibel companding" compressing the signal on recording and expanding it on playback. It was invented by David E. Blackmer of dbx, Inc. in 1971. dbx marketed the PPA 1 Silencer, a decoder that could be used with non dbx players such as the Sony Walkman. A version of this chip also contained a Dolby B compatible noise reduction decoder, described as dbx Type B noise reduction; this was possible after the Dolby patent (but not the trademark) had expired. Software implementations have been developed.

dbx noise reduction, capable of more than 20 dB of noise reduction, was used in the re recording of the film Apocalypse Now in 1979. Dolby A type noise reduction, capable of only 10 12 dB of noise reduction, was used only at the final stage for the mastering of the film's soundtrack to 70mm prints. A modified version of dbx was also used in the Colortek stereo film system. In addition, dbx Type II noise reduction was used in the Model II and Model III variants of MCA's Sensurround Special Effects System on the optical audio track and was a cornerstone of the entire system. MCA's Sensurround+Plus, used on the film Zoot Suit, employed dbx Type II with the 4 track magnetic sound format on 35mm film prints, providing the motion picture with a stereo soundtrack capable of wide dynamic range and freedom from noise.

The first generation Public Radio Satellite System (PRSS), introduced in 1979 and used by the American National Public Radio for delivery of network programming to their member stations via satellite, was a single channel per carrier (SCPC) system that had about 40 dB of analog (recovered) signal to noise. dbx modules that were set for 3:1 were used to increase the dynamic range of the system. Typically this worked well but for some low frequencies the distortion exceeded 10 percent THD. Also the dbx modules varied in how they tracked the compressed audio so the expanded audio was not an exact representation of what was compressed at the uplink. Still, the use of dbx allowed NPR to be known for its high fidelity standards on its satellite system as commercial broadcasters chose NPR to up link a number of commercial radio music programs and concerts by commercial radio networks who demanded high fidelity in the analog era. Many of these problems were resolved when the PRSS moved to their second generation system in 1994, the SOSS (Satellite Operations Support System), in which the feeds were sent digitally.