Very interesting reading.. my god I looked at hundreds of internet pages before finding this gem. Great stuff including use for walkmans , dbx vinyl discs having 120 db dynamic range.
History The Panasonic RQ-J20X portable cassette player from 1982 was the first device to implement the dbx integrated circuit
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.
A miniature dbx Type II decoder on an integrated circuit was created in 1982 for use in portable and car audio, although only a few devices took advantage of it, such as certain Panasonic portable cassette players and Sanyo car stereos. 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. How dbx works dbx Type I and Type II are types of "companding noise reduction". Companding noise reduction works by first compressing the source material's dynamic range (in this case by a factor of 2) in anticipation of being recorded on a relatively noisy medium (magnetic tape, for example).
Upon playback, the encoded material, now contaminated with noise, is passed through an expander which restores the original dynamic range of the source material.
The contaminating signal (tape hiss) is "masked" by the dynamic expansion process, resulting in a significant reduction in perceived noise.
dbx artifacts A sometimes noticeable artifact of dbx was "breathing", as its compander rapidly increased and decreased the volume level of the background noise along with the music, which was most noticeable in quiet musical passages; this was a greater issue with dbx than with Dolby because its compander was more aggressive and worked across the frequency spectrum.
Dolby wins in the marketplace Although it brought extraordinary dynamic range to the lowly cassette tape, dbx noise reduction did not achieve widespread popularity in the consumer marketplace, as compressed recordings did not sound acceptable when played back on non-dbx equipment; Dolby B was already widely used when dbx was introduced. Although Dolby noise reduction also used some companding, the level of compression and expansion was very mild, so that the sound of Dolby-encoded tapes was acceptable to consumers when played back on non-Dolby equipment.
dbx Type I was widely adopted in professional recording, and Tascam incorporated dbx Type II in their Portastudio four-track cassette recorders.
Tascam's Portastudio family of 4 track cassette recorders became an industry standard for small recording studios before being replaced by digital audio tape many years later.
An advantage of dbx Type I and Type II compared to Dolby noise reduction is that it did not require calibration with the output level of the tape deck, which could cause incorrect tracking with Dolby B and C, leading to muffled high tones . However, due to dbx's high compression and strong high-frequency preemphasis, dbx-encoded tapes were, unlike Dolby B, practically unplayable on non-dbx systems, sounding very harsh when played back undecoded.
dbx on vinyl dbx was also used on vinyl records, from 1973 until around 1982, and over 1100 albums were released with dbx encoding, which were known as dbx discs. When employed on LPs, the dbx Type-II system reduced the audibility of dust and scratches, reducing them to tiny pops and clicks (if they were audible at all) and also completely eliminated record surface noise. dbx encoded LPs had, in theory, a dynamic range of up to 120db. In addition, dbx LPs were produced from only the original master tapes, with no copies being used, and pressed only on heavy, virgin vinyl. Most were released in limited quantities with premium pricing. Until the CD format came along in 1982, dbx LPs were the quietest and highest fidelity mass-market audio format available to consumers.[citation needed]
In practice, dbx companders contain electronic noise below about...(and so on)
PICTURES RQ-J20X and PPA-1 portable silencer Site this info from (scroll down 3/4 pagequote:
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The contaminating signal (tape hiss) is "masked" by the dynamic expansion process, resulting in a significant reduction in perceived noise.
Hey John! this Panasonic is a beast, I can see that already. In theory, such dynamic range is better than cd standard.
The dbx nr was clearly a product which involved a deep understanding in human audiology and it required a lot of engineering expertise to develop it. I told you about dbx labs - the company that produces hi-quality microphone preams, dynamics compressors and expanders and all kinds of audio effects processors designed for studio use. I have used some of them when I was into music more seriously than I am now.
But anyway, the priciples on which it was based are far more advanced than dolby b and c type systems. But as always, it was a question of making smart marketing moves rather than giving everything you've got in engineering. I have to hand it to Aiwa. Their last best deck and one of the best decks ever - the XK-9000S implemented dbx in 1992, along with dolby s.
There is a similar parallel in audio cards for computers. While everyone knows Creative Labs and their series of cards (Live, Audigy and now X-Fi), little is known about Aureal 3D with their Diamondmax series of audio cards. back in those days, they were superior in every way - the audio chips, drivers and of course the sound quality and the effects processing. What happened you say? Well, Creative sued Aureal for stealing technology which made no sense because Cretive cards were lightyears behind. The small Aureal could not take it and Creative bought the firm and implemented it's technology into it's own. It's a funny story because I had an Aureal 3D card and after 5 years I bought the newest and the most powerful Creative card - and that was a HUGE disappointment.
Anyway, i would really welcome a dbx capable cassette deck to see what is it capable of. If someone has a dbx cassette deck, please comment on the sound! As far as I know, some Aiwa and Technics decks have it and a guy from whom I bought my own deck swears on his technics RS-B100 with dbx system. He says the dynamics is really good. he said absolutely incredible actually!
Here is some more explaination of dbx systems from this link
AUDIOINVEST.NO WHY DOES LIVE MUSIC SOUND LIVE?
A live performance sound's live because of three basic characteristics of music: tonal balance, spatial perspective, and dynamic range.
Correct tonal balance, or flat frequency response, requires uniform reproduction of sound across the audible frequency range.
Spatial perspective is the dimensional quality of music that allows you to recognize that instruments and voices are reaching your ears at different times and from different locations.
The third, dynamic range, is the difference in volume, measured in decibels, between the loudest and quietest passages of a musical selection. From the 120 dB thundering transients of an orchestra or rock group, to the 30 dB subtle nuances of a triangle or flute.
In order for your stereo system to sound more like a live performance, it has to accurately reproduce all three of these basic characteristics of live music.
When dbx entered the high fidelity scene, audio manufacturers had already made a lot of progress in tonal balance and spatial perspective. So dbx began by addressing the problem everyone else was ignoring: dynamic range.
THE MISSING ELEMENT.
The problem is that conventional records have always been severely limited in dynamic range. Instead of the 90 dB of a live performance, they provide only 50 dB, or 60 dB from the best audiophile discs. Any attempt to record music with greater dynamic range on a vinyl record results in groove excursions simply too extreme for the phonograph stylus to track.
A similar problem exists with tape. Too wide a dynamic range can saturate the tape, causing distortion of the music.
So, audio engineers have been forced to compress dynamic range during recording. They actually squeeze the music, so the louds don't sound as loud as they should, and the softs don't sound as soft. Add to that the problems of record surface noise and tape hiss-which interfere with quiet musical passages - and you can appreciate how dynamic range has suffered in the music recording and reproduction process.
In fact, even with the finest hi-fi equipment and the best conventional records and tapes, you still lose about 1/3 of the dynamic range that was present in the original performances.
THE DBX BREAKTHROUGH.
The breakthrough came when dbx applied the linear decibel companding process to home audio equipment. Because the process not only reduces noise. It also allows the full dynamic range of the source material to be reproduced.
Their first products were tape noise reduction systems used for taping live music without loosing dynamic range.
Then dbx adapted this process to develop a new family of products which you can use to greatly improve the dynamic range of music from conventional records and tapes as well as radio broadcasts. This new family of products is called dynamic range expanders.
But the major goal still remained; to hear the full dynamic range of a live performance from records in your own home.
DBX DISCS: THE STATE-OF-THE-ART IN DYNAMIC RANGE.
Again, linear decibel companding was the answer.
Very simply, dbx went to the source of the problem: the actual cutting of the master disc from which records are eventually made. Instead of arbitrarily compressing or limiting dynamic range as the music signal is transferred from master tape to master disc, dbx precisely compresses the music by a 2 to 1 ratio. The resulting encoded signal fits comfortably within the dynamic range Limitations of vinyl records. Than, when the record is played back through a dbx Disc Decoder, the music signal is expanded in an exact mirror image fashion by a 1 to 2 ratio. This restores the full signal of the music as captured on the master tape.
With dbx Discs, you can hear music with dynamic range equal to that of studio master tapes.
Around 1980, dbx introduced Digital dbx Discs, produced from tapes made by the new digital recording process. The result is the full 90 dB dynamic range of a live performance.
In addition, dbx Discs and Digital dbx Discs virtually eliminate the ticks, pops and surface noise of conventional records. So for the first time, you can listen to the music instead of the record - a major breakthrough in music reproduction.
PERFECTING TONAL BALANCE AND SPATIAL PERSPECTIVE.
dbx was attacking the remaining problems in reproducing sound that approaches the realism of a live performance.
dbx Subharmonic Synthesizer can enhance the bass response of your stereo system to include the natural subharmonics of live music - the kind of bass you actually feel.
And their Computerized Equalizer/Analyzer can provide an accuracy of tonal balance in a listening area never before possible.
dbx linear decibel companding process
The linear decibel companding process, originally developed by dbx for professional tape noise reduction.
dbx vs. dolby
Reduction of noise by three NR systems
TAPE HISS 
Once the signal is recorded by the tape head, the random variation in magnetization from the oxide granules gives a random noise signal up in the kilohertz range called "tape hiss" On the unmagnetized tape, the oxide granules in the tape emulsion are almost completely random, but still have enough magnetization to give you a high pitched "frying" sound if you play the blank tape with high gain.
A persistent random noise signal from the residual magnetization of the oxide granules limits the fidelity of magnetic tape recording. Because of the small size and close spacing of the granules, the noise is of high frequency and is descriptively called "tape hiss". Fortunately, noise reduction schemes such as Dolby and dbx can discriminate against this tape hiss to provide higher fidelity tape recordings.
dbx Noise Reduction
Two inherent problems with recording onto tape cassettes are the limitation on dynamic range for distortion-free recording and the presence of high-frequency tape hiss. The live music to be recorded might have a dynamic range of 70 decibels, but you will do well to get 40 dB of dynamic range recorded on the tape. If you have carefully matched electronics to squeeze or compress the signal to 40 dB before recording and expand it back to 70 dB upon playback you can not only retain more of the dynamic range of the original music but also accomplish some tape noise reduction in the process. Note that soft music signals are made larger than the tape hiss level for recording, and then they are made smaller again on playback. This playback expansion also reduces tape hiss dramatically. Note also that the compression avoids distortion from tape saturation
Thank you Professor John for the lesson about dbx. Very interesting. Did you resolve the issues with your dbx Panasonic?
I had a J20X. Great sound. Was stolen when I was in college. Closest thing to CD when used with a TDK MA or a National Angrom-DU metal evaporated tape (I was lucky to get one from a neigbor traveling to Japan back then).
