I cannot speak to the technical side of this topic either but can confirm that on my system I can definitley hear differences in the overall volume of the music recorded. I always assumed it was a matter of how the music was recorded. I have also noticed that on less than revealing audio systems, the difference in overall volume levels is not as apparent.
CD volume levels
I'm a bit confused by various recording levels I've found on CD's. While most fall in a narrow range of mastering/pressing levels, every so often, I'll run across a CD that was manufactured with a really hot (loud) level, while others are rather anemic (soft). I'm not talking about compression or limiting on the master tape, just the absolute mastering level on the CD. While I understand the physical limitations of cutting vinyl (a combination of science, art, with a little voodoo throw in for good measure), why would there be such a variation in the digital domain? Are there trade-offs with different levels when pressing CD's, just as on the analog vinyl?