It all depends on what was wrong with the original CD master.

Current analogue/digital convertors are far more advanced than those of 20 or so years ago, and so simply re-doing a master leaving everything else unchanged will sound better. This of course only really affects analogue sourced material, stuff recorded digitally can't usually be improved without being remixed.

Often early CD issues were made using second, third or fourth generation copies of the master. Some of these would have also been subject to equalisation and compression, both of which were often needed to allow an album to be cut to vinyl at all. Sometimes this was due to simple laziness, others due to the fact that this was the best copy of the tape that could be found at the time. Re-masters tend to use earlier untreated tapes, sometimes having to acquire them from overseas vaults. Using earlier generation tapes will reduce the amount of hiss and distortion.

Likewise some original CDs may have been prepared from incorrect mixes or takes, or have had the stereo channels reversed.

Mastering engineers can make other tweaks to the sound, fiddling with the balance, tone curve and so on, or adding some compression. Sometimes they go too far and make the recording sound worse than the original. Occasionally there may be some remixing.

Sometimes the remastering engineer will perform some other form of cleanup, removing clicks and other sources of noise, or repairing tape damage. Results here could be variable.

Other remasters throw in extra tracks, ranging from non-album singles, B-sides and other previously released material, to alternate versions, out-takes and other oddities. Some go too far by digging out live material, radio sessions and other crap that really should be sourced from elsewhere or left out all together.

Tweek the sound a bit.
Sometimes sounds better.
Often doesn't.

Can lead to people paying good money for music they already own.

Bizarre.

..trying to make digital recordings sound as good as the records everybody chucked out when CDs emerged.
(..and what JQW said too)

I've got a first generation copy of Echo and the Bunnymens "Porcupine" which is close to unlistenable on my fairly decent stereo system. Decent equipment shows up the poor mastering to an extent that you'd be as well listening to it through an iPod dock.

The recent remaster sorts that out completely. The same goes for the "Love" album with Beatles remasters. Its transformed from a pleasant and familiar noise to proper music where you can hear it breathe again.

Remastering can be a marketing excercise and little more but, in the case of CD's which were issued in the early days of digital, its a neccesity.

possibly apocryphal rockin' soul story attached to the hissing sound on some Sly Stone recordings?

Prince's best work could do with it

I had my iPod on shuffle. A Siouxsie and the Banshees song turned up. It was quite quiet. So I thought to myself that I should volume enhance* the album the next time I plug it up to my computer as it's obviously an old master from the 80's.

So I checked to see what album it was from. It was "Placebo Effect" from Join Hands. The thing is, Join Hands is one of the remastered (2004?) albums I have unlike Peep Show or Tinderbox which were mastered in the 80's.

I think mastering really only effects the volume of a CD (which might not be a good thing). Whatever extra clarity or sharpening of sound that takes place is too subtle to be worth getting excited about.

The following is stuff I like to cart out whenever anyone mentions remastering (and Stimpy has already suggested that I don't know what I'm talking about):

----------------------

Old CDs sound rubbish? Not really. 80's and early 90's CDs are just quiet. All you need to do is turn the volume up. Either manually by turning the volume nob or by using the iTunes volume enhancer*.

Neil Young has the quietest CDs ever released. They were mastered back in the 80's and they seem to sound like crap. Everyone carps on about how bad they are. I did the iTunes volume enhancer on the Harvest album etc and suddenly the songs sound EXACTLY THE SAME as the versions on the loudly remastered 2004 Best Of. The old versions had just as much punch, presence and vitality to them as the remasters. It was as if I was listening to a new remastered copy of Harvest.

That's on an iPod, so I wanted to test my CDs. I played a Joy Division song called "She's Lost Control" that I have on an old 80's album CD and on a recently remastered Best Of. At the same volume they sounded pretty much 99% identical. The 80's CD sounded a tiny bit muffled on the vocals and the drums had maybe 5% less whack to them. And those were the only differences I could tell by playing them back to back with each other. Without the direct comparison I wouldn't be able to tell the difference between the two. If both versions came up on shuffle on my iPod two tracks apart from each other then I wouldn't be able to pick out those differences.

When a song does come up on shuffle that I have on both 80's CD and 00's remastered form, I usually make a guess as to what versions I'm listening to. I then look and 50% of the time I guess wrong.

I repeated the above with "Life During Wartime" by Talking Heads. Vocals and drums sounded exactly the same on both versions.

Remastering is nice but it's not anywhere near as important as most people think it is. You would have to be a real proper audiophile to notice the differences during normal casual day to day playback. All you have to do is put the volume up.

Compare a song from the 80's CD to the 00's remaster. Can you hear a substantial difference?

*On iTunes highlight the album.

Right click and select Get Info.

Under the Options tab there is a volume changer bar.

Drag the volume marker to the desired point on the bar.

Click Okay.

From now on every time those songs play they will always play with that enhanced volume.

----------------

There are two ways to remaster a CD. The usual way (as in 99.9% of the time) is to feed the final mix master tapes into the digitizing machine. The second, and much rarer, way is to remaster the various elements separately and then remix them to make a new master copy with a different mix.

The advantages of remixing are that the sound will be clearer. The possible downside is that as it's a new mix it might sound different to the previous version (such as setting 10 instead of the original setting of 6 being applied to the echo on the lead guitar etc). This can be good if you want to make changes to try and hide dated sounding drums or balance the vocals more naturally with the guitars etc. Obviously a complex song with hundreds of overdubs will be a bitch to remix. If it's a very famous song that people love they might dislike any differences they hear.

The new Beatles remasters are remixes, which is one of the reasons why it's taken about four years to be completed. So the sound quality should be clearer and better sounding. The possible draw back is that the songs might sound different to how you remember and love them.

I'm not saying remastering is bad. I like remastering. I'm just pointing out that it isn't going to make that big a difference to the sound quality in comparison to older CDs that you might be expecting. And if they go the expensive and time consuming direction of doing remixes, then you might not like the end results due to alterations that clash with how you remember a much loved song (Madonna's Immaculate Collection was remixed, or at least fed through the Q sound process, and not everyone likes the work done on that?).

This person goes too far but it's well worth reading this article:
http://www.stylusmagazine.com/articles/weekly_article/imperfect-sound-fo...

http://www.stylusmagazine.com/articles/soulseeking/imperfect-sound-forev...

http://www.barrydiamentaudio.com/loudness.htm

----------------

http://www.stylusmagazine.com/articles/staff_top_10/top-ten-worst-soundi...

"Massive Attack - Collected
This is oh-so-subtle, but it’s annoying. Take your CD of Mezzanine and take your CD of Collected, and play “Angel” back-to-back from one to the other. Notice how on the original album that ominous bass fades in from nothing; sense how deep it goes; see how sharp the rimshot is; feel the air around the bass drum and the shock of the guitars entering. But from this year’s beautifully-packaged Best Of, surreptitiously remastered, the bass is jarringly there from the get go, all width and no depth; the rimshot is flabby and indistinct; and there’s no sense of air or space. It’s like that for the rest of the CD."

I agree, the original album CD does sound better. On the remastered version the bass isn't as deep and the drumming doesn't have quite as much impact. Though you would have to be a person of remarkable hearing to tell the difference without doing a direct comparison with a description of what you're looking for. The point about the opening starting with silence is just that the original has five or so seconds of nothing before the music starts, while on the remastered version the song begins immediately.

Only an obsessive who isn't listening to the song, but only the sound on a technical level, would ever notice and be bothered with these tiny piddly differences. A bass note is a bass note, no matter how deep or shallow it goes.

..re-mixes, then they are not the records we know and love. Even with the same gear (doubtable)and the same personel present (impossible) each mix (especially in pre-computerised mixdown days) is a unique and unrepeatable performance. How on earth is anyone going to re-create the mix of "Tomorrow Never Knows"?
Witness Jon Astleys remixes of "Who's Next" and "Quadraphrenia", not bad but significantly different to the original, especially the latter, and on those LPs, I don't want "different".
Bob Clearmountain's remixes of Free (for a best of) were absolutely appalling, with Simon Kirke's lovely natural sounding immaculately recorded drums replaced by "modern" triggered samples.
Remastering, however,is a complex and delicate process involving a little more than just "turning it up" It involves subtle compression, limiting and EQ as well as (mentioned previously) sophisticated A/D conversion (much better these days than in the first days of CD).