dbx Noise Reduction Units

I fooled around with dbx encoded discs about 12 years ago - in fact I still have a bunch of them. I ran them through a dbx 224x encoder/decoder (which I still have as well).

Compared to unencoded discs, the dbx discs had enormous dynamic range and were very quiet. There was almost no trace of surface noise, and cliks and pops were much reduced in level. Since dbx is a constant slope system (unlike the various Dolby NR systems which perform noise reduction relative to a special referenxce level), one could dub a great dbx encoded cassette by merely feeding the undecoded dbx signal from the disc to the tape deck (with its internal noise reduction switched off, of course).

Though impressive sounding at first, the dbx encoded discs seemed veiled and lacking in transparency after extended listening. I found that I preferred regular unencoded vinyl.

I also feel that Dolby C and S are both better sounding than dbx. However, dbx has one advantage - its 2:1 compression ratio allows you to record more dynamic range than Dolby, thus it may be a better choice for live recording.

BTW, the cassette deck used was a Nakamichi Dragon.

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!