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
Hi,

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.
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