CD vs SACD in STEREO

SACD uses the DSD audio format, which is more analogue and realistic sounding than normal PCM, except that you can't edit the files afterwards, so they are actually only useful for new copies of older tape master recordings, or 1-shot classical recordings.

Both SACD and CD are optical, and therefore give reads that are galvanically isolated from noise.  You can still get that noise-free original read performance by recording audio files onto a blu-ray disk.  You can even record 24/192 or DSD512 sized albums on re-recordable blu-ray disks.  Mine maxes out at only 25GB, but a 100GB disk size (for $100/disk) drive is available for roughly $150.

Optical reads beat all other reads as source by being galvanically isolated data, it only passively reads a light return from the separately powered laser.  Optical files play completely noise-free, and sound like the extroverted original recording compared to hard drive reads.  After hard drives start getting noisier, but optical is too small for a permanent disk, SD cards win the storage noise-freedom award.  Standard SSD's are close, and give the buffer and seek speeds of your dreams, but SD cards are slower versions, that have less noise than any other type of SSD, and give the reads the final bit of extroversion into pure original playback that makes SD cards my choice for reference original reads.

Of course, all files should be played uncompressed from local drives, preferably not from mechanical, as much as they would be perfect in price, performance, and size for way more than just audio.  Mechanical reads have noise added onto them, VS a SSD on the same drive port.  After that, SSD's beat them easily, unfortunately my big 2TB superfast USB SSD that came next actually used more power than a SATA SSD, and then my puny USB thumb drive held the read performance crown until my research proved first that my new SD card and reader's arrival would win the read performance prize.

Of course, you all have to argue that the transport's digital output port quality should come first, and you are right to be talking about optical readers for that first prize.  It's just that a 1TB SD card is so much easier to work with, and I have 5 more slots open on the reader for more 1 or 2 TB SD cards.

"SACD uses the DSD audio format, which is more analogue and realistic sounding than normal PCM,..."

So I assume CD is PCM format, SACD is DSD format. 

Now I can drill down on the ’numbers’ (resolution, frequency range, signal to noise ration, etc). I am using Sony 700 (2nd system) and Oppo 103 for SACD and CD, both using HDMI output. 

And here is what smartypants Allen Iverson (AI) has to say:

When comparing Super Audio CD (SACD) and standard Compact Disc (CD) for 2-channel (stereo) listening, the technical differences are significant, but the audible benefits often depend more on the quality of the mastering than the format itself.¹

Technical Comparison

Key Differences for 2-Channel Audio

• The "Mastering" Advantage: Many audiophiles find SACDs sound better because they are often mastered with more care for a niche market. This typically results in less dynamic compression (the "loudness war" effect), leading to a more natural and "airy" sound compared to the same album on a standard CD.²

• Resolution and Filters: SACDs use DSD, which records the signal at an incredibly fast rate.³ This allows the player to avoid the steep digital "brick-wall" filters used in PCM (CD) playback, which some claim can cause phase shifts or harshness in the high frequencies.

• The "Analogue" Feel: SACD is frequently described as having an analogue-like smoothness, particularly in the reproduction of cymbals, strings, and room reverb. In contrast, standard CDs can sometimes sound "clinical" or "glassy" if not mastered well.

• Hardware Requirements: To hear the difference, you need a dedicated SACD player or a high-end universal player. While Hybrid SACDs have a CD layer that works in any player, you will only hear the high-resolution 2-channel layer on SACD-compatible hardware.

SACD is better than Redbook but much more noticeable with a high end player. Some are surround sound but real music is all 2 channel like going to a concert. I have a Atmos set up for video do not care for it with music.

SACDs generally sound better than Redbook, but format matters less than mastering. For example, Japanese SHM SACDs often sound "bright", sounding anything but "analog".

The other difference maker is the DAC. If you play a great SACD through a mediocre DAC, it won't sound anywhere near as good as a Redbook CD played through a great DAC. 

I only listen to SACDs in stereo or mono. Surround sound is very unnatural. 

Agree that you need good equipment to appreciate the sonics of SACD, but if you have the right equipment most SACDs are a nice improvement over CDs.

The other problem is that unless you listen to classical music, very few SACDs are released and when they are it's in small quantities.  When sold out they increase in price significantly.