I've tried several disc treatments and even with my 40 year-old ears, I can hear slight improvments with each of them. I'm not good at guessing percentage improvements, but it was akin to what you would expect when adding proper isolation devices to your components, or line conditioning, cryo'ed outlets, power cables or other similar tweeks - and relatively inexpensive.
Since we head-fi'ers rate headphones, amps and cables, why not rate disc treatments?
Optrix - 5
Be careful to wipe the disc thoroughly or you may leave a milky (or cloudy) film on the disc surface. If this happens, the treatment can be wiped off with liquid dish soap and then reapplied. This one never did a whole lot for me, but I've rated it as a 5 to provide a benchmark for the others.
Auric Illuminator - 8
A much better treatment IMO, especially the gel that you rub on the disc, which is not very time consuming and kind of fun - like waxing a car that you love. You can skip the black marker trick or just mark the outer edge of the disc quickly. Auric only needs to be applied once on a disc and its effects are there for a lifetime, or so they say, although it too can be wiped off with liquid soap.
Worth trying.
Walker Audio Vivid - 9.5
This is more expensive but seems to trip my trigger better than the others. I paid $50 per bottle and could probably dig up the info concerning the retailer if anyone is interested. I ordered 2 bottles several months ago and have already made it through the first. The plastic bottles arrived in a dehydrated (shrunken in) state so I suppose they sat on the retailer's shelf for a while before I ordered mine - but it works wonders just the same. The advantage of Walker's over Auric was in presenting a deeper, darker background. I'm not sure that this translates into 'tighter bass' as such, but it seems to improve the sense of seperation of instruments which is often hard to pick in headphone rigs.
You can actually use these treatments in conjuction with each other (ie., Auric and Walker's) but I have not tried any such combos yet.
Audio Desk "CD Improver" - 10+
OK, so this is not a "treatment" as such, and you have to be nuts to spend $500 retail for essentially a CD lathe, but my goodness, what a nice improvement! What this does - in lay terminology - is to bevel the outer edge of the CD to create a smoother, easier to read surface? Dunno, but it sure does work. I was lucky enough to find a demo unit, and even then spent a bit more money than sanity would suggest is reasonable - but all of my favorites discs are now getting shaved!
Regarding the Audio Desk CD Improver, I have a duplicate copy of the Acustic Alchemy "Against the Grain" disc in my collection, so I set up an A/B comparison using one shaved and one unshaved disc. Neither disc received any other treatements. So far, 6 out of 6 people have identified which disc is "better" without being told what they were listening for - just to tell me which disc they liked better. None of these people are audiophiles in a remote sense and range in age from 18 to 61. For some of them, I had to play the same track (or even 30 second intervals) several times on each disc before they were sure, but no doubt about it, the sonic improvements are definitely there. I'd say more like 23.9% than 24.1% - no, just kidding.
