dbx Expnders - 3bx, 5bx


This is a new thread which continues from a somewhat unrelated thread that I was pulling off topic.

Hi Sean - re: DBX expanders, three points:

1. The maximum Harmonic and Intermodulation distortion specs for the 5bx are .15%. Which is not small, but it's inaudible compared to the fact that the average vinyl record has had about 30db of compression in the recording and mastering. 30db!!! Now THAT is distortion. If I can remediate that, at a very small sonic cost - for myself, I prefer to. I have tried to hear a substantive enough "negative" difference in a PROPERLY adjusted 3bx or 5bx to know that it's not imaginry, and I can't. But maybe that's me.

2. Expansion/Compression is really a very simple process which in and of itself produces very little in the way of "artifacts". Re-expanding a compressed signal is not a big deal. The only parameters are Transition Level (the db level at which soft is made softer, and loud is made louder etc. and Ratio (the % change to boost or lower volume as a function of deviation from the transition level). As you stated - it's better if you can match the expansion parameters to exactly reverse the compression - but if you can't it's not that big a deal. All you're changing is the relative volumes (amplitudes) of possible related harmonics. You're not introducing phase or time distortion. So you may not be hearing exactly what was recorded, but you're a lot closer than you were listening to the vinyl straight.

In addition - and this is no small advantage - the expansion process by it's nature REDUCES any vinyl noise (which I also consider SERIOUS distortion) very significantly, because it sees it as in the "soft" zone.

3. There is a common misperception that the 1bx expands the entire range, the 3bx expands over 3 freq. ranges and the 5bx expands over 5 bands. This is not true - they all expand the entire spectrum as a whole. The only criteria for expansion are the db levels of the material above or below the transition level. Since the "Transition" level and expansion ratio are user defined, you can get a pretty darn good result. The 5bx makes this very easy, since it has a remote and 5 memory presets. If in doubt - underexpand.

4. They do split the freq. spectrum into bands for the purpose of "Impact Restoration", which seeks to undo the inherently very slow Transient Response of the vinyl media itself and the damage that lazy recording engineers did with Peak Limiters. Now this comes under what you mention as a personal preference - there HAS to inherently be some phase distortion going on here (but again I haven't been able to hear it distinctly.) However they designed these circuits - they did a darn good job. That's the cost. The benefit is the restoration of what a stick hitting a drum actually sounds like. Pop! I'd rather hear that than a phase correct Phoof....

But again - as you said - these are my personal preferences. It's impossible to listen to a vinyl record and hear the "truth". So it is just a tradeoff that I prefer to make. Fix a large amount (about 30%) of one type of distortion while introducing a small amount (maybe 2 or 3%) of another type.
opalchip
Using the dbx products may or may not sound better than the unprocessed music, but they are definitely not uncompressing the compression used in the record making process. Modern recording technique is to use compression and limiting at multiple stages during the recording process. The key parameters for a compressor are threshold (the level at which the compressor circuit kicks in), ratio (the amount of compression applied) and attack (how quickly the compression occurs). To accurately undo the use of a compressor you would have to know the exact setting of all these parameters. A simple expansion circuit cannot undo a single compression effect let alone multiple compressions.
Every DBX unit I ever heard, made a "breathing" sound that was audible, while it did its thing of expansion.

Not for me, thanks.
Twl...Too bad. Do you realize that most of the analog tape masters, which audiophiles extol, used DBX noise reduction. It was better than Dolby, which the rest of the master tapes used.
"Pumping" or "breathing" is a sign of over-expansion i.e. the threshold for the peak unlimiter is set too low. As such, the expander is trying to expand peaks that aren't there, resulting in the audible noise and distortion. This is why Opalchip recommended conservative adjustment of the expander i.e. "under-expansion" to avoid these problems.

Opalchip's other comments in section 3 about "not breaking up the spectrum" is kind of deceiving in itself. As he mentions in section 4, "impact restoration" can be adjusted by manipulating the controls. Given that the "impact restoration" is a direct result of varying the amount of expansion taking place over a narrow bandwidth, the spectrum really is broken up.

In that respect, one can "somewhat" fine tune the system for more natural results with a 5BX than they can with the lesser 1BX or 3BX. This has to do with being able to juggle the ratio of primary to harmonic expansion, not only on the whole, but recording by recording through the use of the multiple memory positions and the remote control.

As Eldartford commented, Bob Carver came out with the Autocorrelator to reduce surface noise and the Peak Unlimiter for dynamic range expansion. Only problem is, he incorporated them into very noisy circuitry of his flagship Phase Linear 4000 preamp, therefore negating the possible benefits that these circuits may have brought with them. He also sold these as a separate add-on box under the Phase name, which i "think" was a model 1000 Autocorrelator. I've never tried using the Carver circuitry outside of the original Phase 4000 preamp, so i don't know how well it would work with higher end gear.

As to the RG unit that Lugnut mentioned, this was designed by Robert Grodinsky. Robert was a very intelligent audio engineer that, much like John Curl, designed quite a few products for various manufacturers over the years and later introduced their own product line. Some of his products are still floating around in the used market and many of them are quite solid designs. Due to their age and advances in raw component technology, they would probably cost a small fortune to upgrade to current standards. Then again, one could buy a current "state of the art" component and end up spending the same amount upgrading the caps, diodes, etc... as they would with Grodinsky's designs. I've taken the liberty of including a list of some of the major audio related patents that Grodinsky received over the years below.

As to DBX type products, the best that i ever heard one of their expanders sound was in a system that had Bose 901's as the speakers. Due to their design, 901's tend to compress the audio spectrum. As a result of this compression, they tend to sound somewhat "flat" and lacking in punch. The addition of the DBX processor ( 3BX ) to this system made a huge difference. Bass was much fuller and the treble actually had "sparkle" to it, which is hard to get from older 901's. I found it to be a worthwhile addition to this system and so did the owner of this system.

Having messed with multitudes of different expanders and companders ( combination compressor & expander in one unit ), i've never really much cared for their use in a high end system. My thoughts are that they work much better in lower grade systems with electronics that lack speed and transient response. It is due to this lack of speed that the existing peaks and dips on the recording aren't fully reproduced, making the additional expansion both more noticeable and beneficial to system performance and listening enjoyment. Obviously, this is just my opinion though.

As to the DBX encoded records, it is too bad that this type of processing didn't take off. Due to the lack of available material that anybody wanted to listen to, and the fact that you had to have a DBX decoder to enjoy them, the idea was lost before it had much time to really get any type of momentum going.

As a side note, most modern day "rock" type recordings typically have about 5 - 10 dB's of dynamic range at best. Some severely compressed "rock" recordings are actually closer to 3 - 5 dB's of dynamic range. When recordings are this heavily "squashed", dynamic range expansion is both more beneficial and harder to properly set. That is, the unit will pretty much be trying to expand everything fed into it since EVERY peak and even non-peaks that simply maintain a higher than average amplitude are compressed. I haven't messed with one of these units in a long time, but if recordings continue to go in the same path that they have been for some time now, i may be checking one out sooner rather than later. Luckily, many of the recording engineers themselves are starting to complain to the record companies and record producers that TOO much compression is being used, so we may see some improvements in this area. Let's hope so. Sean
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U.S. Patent No. 3,980,964, 09/14/1976 (app. 06/20/1975, serial 588,604) NOISE REDUCTION CIRCUIT (class: 330/278; 330/59; 330/136; 330/141; 330/144; 330/149, international: H03G 003/30) Grodinsky; Robert M. of Skokie, IL [Pt-Txt43KB] [DjVu135KB]

U.S. Patent No. 3,992,585, 11/16/1976 (app. 10/06/1975, serial 620,537) SELF-ENERGIZING ELECTROSTATIC LOUDSPEAKER SYSTEM (class: 381/110; 381/116; 381/191, international: H04R 003/00) Turner; Jacob C. of Milwaukee, WI and Elliott, Douglas M. of Milwaukee, WI and Grodinsky; Robert M. of Skokie, IL and Mills, Thomas F. of Chicago, IL (assignee: Koss Corporation of Milwaukee, WI) [Pt-Txt26KB] [DjVu135KB]

U.S. Patent No. 4,162,457, 07/24/1979 (app. 12/30/1977, serial 866,021) EXPANSION CIRCUIT FOR IMPROVED STEREO AND APPARENT MONAURAL IMAGE (class: 330/295; 330/124R; 330/278; 333/14; 381/28; 381/107 - international: H03F 003/68) Grodinsky, Robert M. of Skokie, IL 60076 [Pt-Txt39KB] [DjVu144KB]

U.S. Patent No. 4,312,060, 01/19/1982 (app. 04/26/1979, serial 033,380) PREAMPLIFIER FOR PHONOGRAPH PICKUP (class: 369/134; 330/302; 369/88 - international: G11B 003/00; G11B 003/74; H03F 003/04) Grodinsky; Robert of Skokie, IL [Pt-Txt36KB] [DjVu119KB]

U.S. Patent No. 4,500,850, 02/19/1985 (app. 10/22/1981, serial 313,658) AUDIO AMPLIFIER APPARATUS WITH MINIMUM NON-LINEAR DISTORTION (class: 330/307; 330/66 - international: H03F 003/04) Grodinsky; Robert of Skokie, IL [Pt-Txt38KB] [DjVu128KB]

U.S. Patent No. 4,594,561, 06/10/1986 (app. 10/26/1984, serial 665,049) AUDIO AMPLIFIER WITH RESISTIVE DAMPING FOR MINIMIZING TIME DISPLACEMENT DISTORTION (class: 330/297; 330/149 - international: H03F 001/30) Grodinsky, Robert M. of Skokie, IL and Cornwell, David G. of Chicago, IL [Pt-Txt33KB] [DjVu111KB]

U.S. Patent No. 4,597,100, 06/24/1986 Ultra high resolution loudspeaker system Grodinsky; Robert M. and Cornwell; David G. (assignee RG Dynamics, Inc.) [abstract] [DjVu149KB]

U.S. Patent No. 5,070,530, 12/03/1991 (app. 03/25/1988, serial 173,435) ELECTROACOUSTIC TRANSDUCERS WITH INCREASED MAGNETIC STABILITY FOR DISTORTION REDUCTION (class: 381/422; 381/412; 381/421 - international: H04R 025/00) Grodinsky, Robert of Skokie, IL and Cornwell, David G. of Chicago, IL [Pt-Txt35KB] [DjVu123KB]

U.S. Patent No. 5,357,587, 10/18/1994 (app. 12/23/1992, serial 995,833) DISTORTION REDUCTION IN LOUDSPEAKERS (class: 381/414 - international: H04R 025/00) Grodinsky, Robert M. of Skokie, IL and Cornwell, David G. of Chicago, IL [Pt-Txt31KB] [DjVu146KB]

U.S. Patent No. 5,386,474, 01/31/1995 (app. 08/17/1993, serial 108,092) AMPLIFIER-SPEAKER INTERFACE CORRECTION CIRCUIT (class: 381/28; 381/93; 381/94.9; 381/300 - international: H04R 025/00) Grodinsky, Robert M. of Skokie, IL and Cornwell, David G. of Chicago, IL [Pt-Txt23KB] [DjVu109KB]

U.S. Patent No. 5,982,905, 11/09/1999 (app. 01/22/1997, serial 787,122) DISTORTION REDUCTION IN SIGNAL PROCESSORS (class: 381/94.1; 381/394 - international: H04B 015/00) Grodinsky, Robert M. of Skokie, IL and Cornwell, David G. of Chicago, IL [Pt-Txt82KB] [DjVu215KB]

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