JSP: unless mastered by John R.T. Davies, Ted Kendall or Chris King the releases I've heard sounded awful to my ears, plus the fact that they have often "borrowed" masterings other labels like Bear Family paid for and did the research for.
Jasmine: lots of noise reduction on at least some of their releases.
Real Gone: there were two labels with that name, Real Gone Music, based in the US, that only reissues licensed material, and the EU public-domain label Real Gone (no "Music" in their name) with cheap, non-licensed reissues taken from existing sources like LPs and CDs.
Ace: I've not always been happy with the sound on their (licensed) reissues, it was sometimes too "pumped-up", too loud and harsh. Others like it that way.