dbx Noise Reduction Units

The last reply jogged my memory - There were two dbx systems, type I and type II. Type I was intended for open real tape and used a wider bandwidth into the compression control channel and less eqaulization. Type II was intended for cassette, LP, and other consumer applications.

Both types use a 2:1 compander scheme with a constant slope - there is no reference level where dbx changes its behavior. This is in contrast to Dolby B,C and S which do very little to the signal once it passes the reference level (the Dolby double D on your cassette dack level meters), and increase the compansion effect as the signal becomes smaller. Thus recorder/tape calibration is critical.

The Dolby systems focuses on one or more sliding frequency bands depending on the type (B, C, S). dbx runs broadband.

Dolby seems to do less to the signal than dbx, which probably accounts for my feeling that it's more transparent. If you doubt this, try playing back and undecoded dbx signal - it's unlistenable. In contrast , an undecoded Dolby B, C, or S signal, while sounding strange, will still be listenable.

The dbx massive 2:1 constant slope compansion sometimes results in audible breathing as noted by previous reply.

-- from the store of now useless knowledge!

ghostly,
youve almost got it right.
typeI: variable compression/expansion, can be used as peak limiter/unlimiter also.
type II: fixed 2:1 comp/exp, ONLY for record/playback of tape (better for reel, not so good for cassette) and playback of dbx LPs (would have been stiff competition for cd, dead quiet).
dolby s: the most effective tape noise reduction made. dead quiet clear accross the freq band. bad timing kept it from competing with cd.
.......regards.....tr

Hi, I tried the Type II ages ago and soon threw them out. They did reduce noise but together with it much of the inner life of a recording. Subtle dynamic nuances and changes were just blotted out. What was worse, they seemed to add something to the music, which could best be described as breathing, which was very annoying and distracting from the musical enjoyment. Here in Europe they were made and distributed by Nakamichi under licence, but for the reasons described above, they never were a success amongst the cognoscienti.

Detlof you have it right on the money regarding the DBX scene. The very best cassette decks ever made (Tandberg 3004 and Nak 1000ZXL), were always best with the Dolby left off no matter what tape formula was used I, II, or IV. There was degredation to the sound regardless of what NR was chosen. I felt that Dolby and DBX systems were only needed in the very early cassette era, when S/N ratios were down in the low 50db range. As the metal tape era dawned (1979/80), and S/N ratios improved, hiss levels reached an acceptable level. This is a perfect example of adding stages of circuitry and moving backwards.......Frank