That is a loaded question. SACD stands for Super Audio Compact Disc (I think). Of which there are several types:

Single layer: playable only on SACD players (earlier SACD discs were this) . Dula layer: has both SACD and CD content, playable on both CD and SACD players (most newer SACD discs)

To that there are:

Two channel stero

Multichannel - surround sound 5.1 (5.1 means Center Front Speaker, Left and Right Front Speakers, Left and Right Rear or Side Speakers, and a subwoofer)

SACD players are often bundled with DVD players which are intended to be used in a surround sound home theater. I'm not sure if you can get a SACD player that is NOT a part of a DVD player. But not all DVD players are SACD players.

As far as the sonic qualities, here you should do some research to verify what I'm going to say:

SACD has a sampling rate greater than that of typical CDs. Imagine the difference between a document printed at 100 dpi and one at 1200 dpi... now apply that to music. Actually, 300 dpi vs 600 dpi may be a better comparison. You can read both, but upon close inspection, one is a lot sharper.

There is a competing format called DVD-Audio, or DVD-a. These are DVD's, and cannot be played on a CD player. They too have a greater sample rate. However, in order to hear the higher sample rate, you need a DVD player that is compatible with DVD-a. Again, not all DVD players are DVD-a players.

There are very few players that are both DVD-a and SACD compatible. However, you can listen to DVD-a discs on a normal DVD player, but not at the higher sample rate... but you do get the surround sound 5.1 advantage.

I do not have a DVD-a player, but I do own a couple DVD-a discs, and they do sound a LOT better than their original recording.

As far as I know, there are no car SACD or DVD-a players... maybe next year...

Now, in addition to the sonic "superiority" of these formats over those of CD's, as has been hinted at, these recording usually sound so much better because they have been re-mixed and digitally mastered. As a result, you can listen to these discs in regular CD players (for dual layer SACD) or regular DVD players (for DVD-a discs) and usually they sound a LOT better than their original. USUALLY... the remixing and remastering processes vary. A LOT depends upon the quality of the original master tapes, and the quality of the recording equipment recording environment they were recorded in.

There is software that can take an old faded and cracked and ugly photograph and make it look brand new. The same type of software can improve audio recordings. This software is getting better every year. But, you can't make a silk purse from a sow's ear. I have a good sound card and program to declick and denoise LPs to make CDs. A friend let me borrow an old Led Zep bootleg album to try to clean it up... again, there are limits as to what you can do. Often the limit is how much time do you want to spend on such a project... after cleaning up an album, having listened and mbuttaged the recording over and over I never want to listen to it again... or at least for quite some time.

Which brings up the question: where do you draw the line between an original and a result which is better than the original? I would love to hear some of the old recordings made back in the earlier part of the 1900's cleaned up and made to sound like they were recorded yesterday, but you would end up with something that is more one person's interpretation of what the original sounded like than the original. I guess it's up to the listener to say if they like it or not. If the person making those interpretations is the original artist, then I guess its OK. If not, well, that is up to the listener.

Now, some opinions on a couple of SACD's and other re-mastered re-mixed albums I own.

Pink Floyd Dark Side of the Moon - AWESOME! Yes, it aint bluegrbutt, but this is a perfect example of hearing things clearly that you just barely heard before.

Nickel Creek and Chris Thele's albums - GREAT! In surround sound it's like you are sitting in the middle of a circle with them playing around you.... almost at least. In surround sound, the central point is the center speaker, then the front left and right speakers, then the rear left and right. Those instruments secondary to the lead instrument(s) often come out strongest from the rear speakers. As a result, as the musicians swap to dominant position, the likewise swap from back to front speakers... not a problem to me. Like musicians moving around on stage to swap central mike position.

Carol King's Tapestry - Single layer SACD (won't play in CD player) Not so good. The recording still sounds muddy to me. A disappointment.

Eagles' Hotel Callifornia DVD-a - AWESOME, even when only played in standard DVD player.

Steely Dan and Donald Fagan DVD-a - Again Awesome!

Steely Dan's Gaucho SACD - I like it a lot, but some comments from people a lot more familiar with the album than I don't like some of the more radical re-mixing over the original. If you have listened to an album 100 times over the past 20 years, you might get upset to find the lead instruments changed, and the drums more heavily emphasized.

Now one re-mastered album I purchased that I regret buying is Nitty Gritty Dirt Band's Will The Circle Be Unbroken (the first one) (Regular CD - remixed). The problem I have with this has mainly to do with the spoken parts of the album, which make the album as special to me as the music... the removal of tape hiss between conversations is a bit annoying... you hear it go up and down between pauses... to me it is distracting. Also, the added tracks by themselves do not justify buying the newer version. With the noisy environments in most of today's cars and trucks, you will not notice the difference between SACD and MP3... with stock radio-CD player-speakers. I recently replaced my stock sound system with new speakers, receiver, and power amp. At first, I thought "this sounds terrible, I'm going to take it back". Later, playing SACDs I found that the problem was not in the new system, but that it showed the flaws in the old recordings, as well as the broadcasted music. I guess this should serve as a warning to anyone making a serious upgrade of their sound system (applies to HDTV too): the higher definition brings out the flaws as well as the good sound. After awhile, you find the flaws in older recordings to be annoying. Yes, I know what you mean. I only wish Kashmir had been recorded with more modern recording methods and equipment!