Short answer: I own numerous classical SACDs, and 24bit/192kHz (PCM) FLAC downloads, and Blu-ray, plus a few Pure Audio Blu-ray, and Ultra HD Blu-ray, that are based on modern high-quality recordings, and all of these “hi-res” technologies are capable of excellent audio quality.
Before I get into a lengthier discussion of audio quality, I’d like to point out that there are other factors affecting the selection of consumer deliverables:
- After listening to numerous multi-channel classical SACDs, plus numerous multi-channel Blu-ray classical, opera, and ballet recordings, I have concluded that multi-channel can be useful for classical music in an installation where the main L & R speakers must be widely spaced. (OTOH, in a small room where the main speakers are spaced 5 feet apart, there is not much benefit IMO to a center channel and surround speakers.)
- HD video is indispensable for ballet, very useful for opera, and an enjoyable enhancement for classical music recordings.
- I think that Pure Audio Blu-ray discs are particularly well suited for very large remastered "box sets", such as the Maria Callas studio recordings that were released as 69 CDs. It would probably take quite a while to download all of the Callas recordings in 24/96 FLAC. I think that releasing it on 69 CDs (30+ year-old digital storage technology) was not ideal. A few Pure Audio Blu-ray disks would have been better IMO.
- Ease-of-use is a matter of personal preference. Some people think that downloads are easier, whereas some like the simplicity (and reliability) of dropping a disc into the tray and hitting the “Play” button.
- One disadvantage of SACDs is that the SACD layer cannot be played on a PC. (The CD layer of a hybrid SACD disk can be played on a PC.)
- Often SACDs (e.g., from Amazon) are cheaper than hi-res downloads (e.g., HDTracks).
Regarding audio quality of hi-res DSD vs. FLAC, following are my quick, preliminary thoughts regarding a complicated topic.
As a classical music lover, my criterion for assessing the quality of a recording is fairly simple: Does the recording sound like what I remember hearing in the symphony hall or opera house (where no electronics are used – no sound reinforcement – the sound is 100% natural). I recognize that memory is fallible – nonetheless this is my criterion. And I want any deviations from a live performance to sound pleasant vs. unpleasant.
I’m not interested in a comparison test procedure that uses PC software. I’d want to know the quality of the original recording, and mastering. (Garbage-in/garbage-out.) I’d want to know whether or not the test files were manipulated by software, and if so what artifacts of the software might affect the sound quality. And I’d want to know whether or not these files have any relevance to consumer deliverables that I might buy (e.g., CD, SACD, Blu-ray, high-res FLAC or DSD download). (I’m not going to use PC software to play music – so I don’t care what PC software sounds like.) I am only willing to listen to music that I like (which eliminates some tests I’ve read about). The good news is that I listen to music performed with no electronics involved, and I know what classical music sounds like performed live in its intended venue. (I have full season tickets to the symphony and opera, plus I attend several small-scale chamber performances every year. That’s how my ears are “calibrated”.)
A complicating factor in comparing different deliverables of the same recording is whether “bass management” or a “.1” channel is used to send low frequencies to the subwoofer. (IME these different methodologies affect the sound quality.)
Sound pressure level matching between different recordings is important when performing qualitative comparisons, and is difficult to guarantee. (I don’t own a sound level meter.)
Based on the equipment that I own, the ideal methodology would probably be to use two Oppo UDP-205 universal players, with each connected to different line-level inputs on a modern integrated amp that can switch inputs via the remote control. An SACD loaded into one UPD-205, and a 24/192 FLAC playing on the other UDP-205. However – at least today – I’m not willing to uninstall one of my UDP-205 and lug it into the room with the other UDP-205. The next best arrangement is probably to have an SACD in the disc tray, and have a 24/192 FLAC file of the same recording on a USB drive, and switch via the Oppo’s “Home” menu.
The good news for me is that recent performances of classical music are routinely captured and offered in hi-res audio. I’ll have to peruse my collection to see which recordings I have in SACD and 24/192 FLAC. I can think of only one: Reference Recordings RR-136 Saint-Saëns: Symphony No. 3 "Organ" (Kansas City Symphony). I just acquired “The Asia Tour” featuring Sir Simon Rattle and the Berliner Philharmoniker that came with SACDs and Blu-ray video (recorded in 24bit/96kHz PCM), but I’m having difficulty downloading the FLAC 24/96 files. (I could compare the audio quality of the SACD with the Blu-ray.)
My approach to listening-test-methodology would be to make informal listening impressions, where I control switching back and forth. I understand the concepts of ABX, and double-blind testing, but I’m not interested in spending time attempting to implement these methodologies.
Bottom line, making valid comparisons between DSD (e.g., SACD) and 24bit/192kHz PCM (e.g., delivered via FLAC download) is not a straightforward task.
FWIW, here’s my perspective. For the music that I like, there are many modern performances that were captured in hi-res audio (DSD or PCM) – and in a growing number of cases - Blu-ray (or Ultra HD Blu-ray) audio/video. Almost all modern performances were recorded in hi-res. My perspective is this: Why not buy the consumer deliverable that is in the same format that the recording was mastered in – vs. buy a version that was downgraded (and possibly transcoded) into 30+ year-old CD storage technology?
Perhaps over the next few days I’ll do some informal listening comparisons. For now, I can say that both SACD and 24/192 (and 24/96) FLAC are all capable of excellent audio quality. My favorite way to consume music is Blu-ray audio/video featuring hi-res surround-sound and HD video, followed by surround-sound SACD. (Ultra HD Blu-ray recordings are slowly becoming available for classical music, opera, and ballet.)