There is a great writeup at Amazon.com where someone A/B compared the "regular" release of Joshua Tree with the MFSL release.
Here it is...
Sonic improvement, but worth the price? January 19, 2007
Reviewer: Giacomo Holdini (Minneapolis, MN)
Since many other reviewers have amply debated the artistic merits of this album (the phrase, "beating a dead horse," comes to mind), I'll direct my review solely to those people considering purchasing the MFSL version, who might be wondering if it offers any sonic improvement over the standard CD version of the album, and, if so, if those improvements are worth the price of purchase.
There is no question that the sound on this MFSL release is an improvement over that on the Island Records CD, still featuring the original 1987 mastering, done when the album was first released. However, the improvements on the MFSL disc are subtle. The most noticeable difference between the two discs upon first listen is the difference in volume; the MFSL disc is decidedly louder. I decided to rip a few tracks from both CDs into waveform and then compare them in a wave editor to see just how much louder the MFSL disc is. The MFSL's signal gain is roughly 60% greater than that of the original CD. If one were to compare the two discs without compensating for the difference in volume, that difference would contribute to the perception of improved sound quality in the Gold version. This perception is not entirely inaccurate, however; the signal-to-noise ratio on the original version is lower, and by increasing the volume of the original version to match that of the Gold version, one is also increasing the base noise level. There is noticeably less background noise on the Gold version, even when played at higher volume levels. This helps present a cleaner sound picture. That aside, once I compensated for the volume difference, I really had to focus closely to hear the differences in sound between the two discs. The MFSL disc has consistently cleaner, more focused, more dynamic sound than the original, and generally sounds like a higher quality mastering, but those differences presented themselves to my ears only upon close listening on high-end equipment. In many "real world" listening situations, and on anything other than high-end equipment, the differences will be subtle, to say the least, and quite possibly unnoticeable.
The MFSL mastering does not improve the basic quality of the recording or the mix, which is still dense with atmospherics and highly ambient. Reviewers who complain about the sound quality of the original disc and blame it on old mastering techniques may have missed the mark: U2 specifically asked engineer Flood for this kind of sound (as he explained in the "making of" DVD), and as such, I suspect a lot of what is considered poor mastering is actually intrinsic to the original recording. The MFSL version does not alter that. It just presents a slightly cleaner, more accurate version of a rather murky soundscape.
So, is it worth getting? Cost and availability notwithstanding, this is definitely the better CD version of the album to have. However, those expecting miraculous improvements might find themselves disappointed. The diminishing returns theory applies here: you will spend a lot for incrementally slight improvements. Moreover, Island Records can't hold out forever; one of these days, they'll likely issue a remastered version of The Joshua Tree, one which most likely will improve on MFSL's nearly two-decades old mastering, for a much lower purchase price. (This goes double in the unlikely event that the album will have been remixed for re-release.) Until that time comes, the MFSL version is the best one out, but given the cost, I suspect only collectors or those whose ears are extremely particular would find it to be a worthy investment.
