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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
eldartford
4,262 posts
 
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.
lugnut
1,190 posts
 
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.
onhwy61's avatar
onhwy61
5,261 posts
 
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.
eldartford
4,262 posts
 
Onhwy61...Did you ever hear DBX encoded records? If not, research them.
twl
3,251 posts
 
Every DBX unit I ever heard, made a "breathing" sound that was audible, while it did its thing of expansion.

Not for me, thanks.
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