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.

I realize your question was for Sean but I'd like to share my experience with you. At one time I had a moving magnet cartridge on my LP12 that gets a lot of good press here on Audiogon and which is a fine cartrige BUT it enhanced surface noise during low levels to an extent that really annoyed me. I was reluctant to put this new cartridge away and step up to a new moving coil. My local audio salon allowed me to audition the DBX line as well as another device that was much better and which I bought. Sorry, I have forgotten the name of it but will post it later in this thread when my sister, who I gave it to emails me with the name.

One problem with your posting is that you don't seem to take into account RIAA equalization which increases the bass and decreases the highs back to the correct levels of dynamic range.

Back to the device. It certainly made all the low level surface noise go away but it also reduced the low level musical nuances too. The increased dynamic range was enjoyed on some very compressed recordings but was unnatural with most.

As far as I'm concerned and based on my experience there is just as much dynamic range on lp's and sometimes more, much more as compared to CD's. The answer to your problem is a table that is good enough to allow a better tonearm and cartridge to transfer the signal properly. The wrong table will just accentuate noise and degrade the signal. Proper care of your records...washing, vacuum drying and polyethylene sleeves and a carbon fiber brush is all you need. Of course, a reasonably good phono stage is a must as well and it must be matched with whatever cartridge you are using.

To summarize I believe you would be taking a big step back which will solve only one of your problems and introduce others which will annoy you upon long term listening. If this wasn't the case then there would have been a huge demand for these cheap little used units you refer to. The analog purists figured this out long ago and considering myself to be among them I urge you to go in a better direction. Of course, what you propose is a pretty good short term solution for what I believe will be very little money. Your choice, and I certainly didn't want to beat up on you, but I clearly do not agree with your 30 db dynamic range accusations in the real world of listening.

I just remembered the name of the much better expander. It's a by RG. There is one on eBay guaranteed to be not DOA with bidding at $5. This is the top of the line model being a Pro and just blows away the DBX line.

For the record I've kept this thing in the family giving it to my mother to use with her B&O to great benefit until her death and my sister is now using it with her tv tuner as some television signals have a lot of low level noise. She loves it but it does surprise me that she can hear those low level whispers in movies. I used it for about six months and tired of it in about three electing to go with a nicer cartridge which solved my problems entirely.
Hi -
Part of the problem that you had may have been that you went with the RG. Somehow it may have sounded better in the audition circumstances, but it is totally inferior to the DBX (5bx especially). You can't even alter the transition level on them. DBX (and it's "Over Easy" algorithm was and still is one of the studio standards in EQ and Compression/Limiter technology.
A 5bx with remote control in pristine condition goes on Ebay for usually between $1500-$1900. And they rarely come up. (These are not being bought by guys with cheap turntables.) RG's go for $40-$60 - there's a reason for this difference in value.

(Leaving the house now - I'll check in again on Monday.)
Opalchip....DBX certainly perfected the use of compression/expansion to overcome analog tape recorder noise. They lost out to Dolby labs because of stupid marketing decisions having nothing to do with technical merit.

I do not think that one-way expansion of dynamic range is effective for noise reduction, although you may like it for other reasons. The Phase Linear Autocorrelator (one of Bob Carver's better ideas) is much more effective. (It is a very clever dynamic multiband filter).

The DBX application that I found to be very effective was the DBX LP system, where the recording was very much compressed and use of the complementary DBX expander was essential for playback. Noise reduction was only one benefit. Phono pickup performance was also improved by avoiding any highly modulated grooves. Based on response to prior postings, I must be the only guy who ever experienced this system.
Eldartford is right but there wasn't a corresponding amount of software offered so a superior system again bit the dust. Also, you may be right about the RG vs. the DBX units but not in my experience because I used everything mentioned except Eldarfords piece. Anyway, noise is not an issue with my system and I don't have much money tied up in it. Also, nobody I know that has a better to reference analog front end needs such a product. Sure, there's an occasional imperfection of a click or pop but surface noise is very close to as black as CD and in most cases it surpases CD in total dynamic range. Hey, nothing we can buy is perfect so there are many imperfect choices we can make. The digital guys will not agree about the dynamic range which is fine and a lot of it may be due to intentional compression imposed by either the artists or the engineers who typically do their thing based on car audio. Each to his own. And, if this is what you want to do go for it. It seems your mind is made up anyway.
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.
Onhwy61...Did you ever hear DBX encoded records? If not, research them.
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

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]

Sean...The main problem with dynamic processors of all kinds, noise filters, expanders, multichannel logic decoders, is the fact that their action is controlled by the audio signal, so there is always some delay before they act. The usualy listener complaint is "pumping". Digital technology could eliminate this problem, by delaying the signal for a few millisconds so as to give the processor time to figure out what to do. Then, the processor action could be introduced at exactly the right moment.

The phase 1000 Autocorrelator did several things.
1. Dynamic rumble filter (switched out when audio signal had LF content).
2. Dynamic Multiband HF noise (scratch) filter.
3. Dynamic range expander with very slow action to match human gain riding. It was not designed to undo electronic compression.
4. Peak unlimiter.

It was specifically aimed at LP problems, and it was good for everything except clicks and pops (for which another outboard processor could be used). My complaint was that it did need to be tweeked up for each LP, and that was a nusiance.
Eldartford, I concur with your analysis of the Auto Correlator, since I have been using the Series II since 1991. I used the series I before that, since 1980 or so. I use it primarily for dynamic restoration on records and as you have mentioned it was necesary to change the settings for each record, but I have persevered and have marked all of my records with the settings to be used! The unit does not exhibit any "pumping", but the restoration of about 10db dynamics on classical recordings is quite beneficial, IMO. The slight reduction in noise during quiet passages is also appreciated. I rarely use the auto-correlation, since my records are in good shape, but it is useful on noisy radio broadcasts.
El: the fact that dynamic processors respond AFTER the fact is why i said that they aren't suitable for high end systems and work better with lower grade components. With lower grade components, which are typically bandwidth and transiently challenged, the lack of speed typically isn't noticed as much. As such, "slow" remains "slow" and you end up with an increase in dynamics. This is not the same thing as "fast" becoming "slower" with a smaller increase in dynamic contrasts. Sean
Sean...No disagreement that existing dynamic processors (which I know of) always are slightly behind the signal. However, some are much better than others in this regard. Bob Carver's toy was pretty good, as inpepinnovations@aol.com reports. My point is that digital technology affords the oportunity to overcome this problem, but then digital recordings don't (from a technical standpoint) need the kind of compression that calls for expansion on playback.
inpepinnovations@aol.com...The Autocorrelator control signal is LEFT + RIGHT, (Mono). The dominant FM radio noise is in the LEFT - RIGHT multiplexed signal which is mixed with the Mono so as to derive LEFT and RIGHT. Therefore the performance of the Autocorrelator is not good with FM radio. If you can figure out how to do it you might invert one channel going into the autocorrelator, so that the control signal becomes L-R, and therefore a good indicator of noise.

I once had two Autocorrelators, for the front and rear channels of a matrix quadraphonic setup. Of course with LPs it is the L-R signal (vertical groove modulation) that has the big noise problem, and I modified one of my units in this way for the rears.
Kind of funny how digital is supposed to have "sooo much more" dynamic range, yet the current batch of recordings use more compression than ever. Talk about a paradox!!! Sean
Sean...That's what pop music fans like. The customer is always right. Real audiophiles listen to classical.
Very interesting discussion regarding compression - I had an early DBX which I used with a R2R for noise supression. Question, what percentage of audiophiles do you suppose really have equipment and a room in which you could play music uncompressed? Few, I think.
I've just picked up a single band dbx 228 expander. I'm very impressed, especially with FM, which I listen to a lot. However, it doesn't have the impact restoration feature but it does have the dbx decoder - now to find some encoded LPs.

It also works well on most LPs and many CDs. For SACDs, it can help some, especially if the original recording has tape hiss and/or was compressed somewhere in teh production signal train.

So far, as long as I don't overdo the expansion, I'm not hearing artifacts that detract - the cost/benefit ratio is favorable. Even though there have to be lots of old op amps in the 228, it adds little of that annoying "op-amp harshness."
Somsel... DBX LPs had the misfortune to arrive at the same time as CDs. Their improvement over regular LPs is large. Focus is mostly on noise reduction, where that compares with CDs, but there are other advantages. Most important IMHO is that performance of the phono cartridge is greatly improved because groove modulation is always in the "sweet spot" for the cartridge. No hard to track passages or imposible to track peaks. Also,because of closer groove spacing playing time is increased.

I have a few of these LPs, but you won't get them! I keep them for demos. Unfortunately there were few recordings issued, and the performances were not the best.
Want a DBX compressor expander? I have one WITH the DBX disk exander circuit built in. PM me if you are interested. I have no idea if these disks are available or where or at what price.
I think it is a 20bx? Can't 'member the model number. I used it a long time ago with a Tandberg reel-2-reel.

I don't know if you can call compression 'distortion'.