Is high-resolution audio (like SACD) audibly better than than CD?

Some technical debates are so polarised that it is hard to believe there can be sane people on both sides. One such is that over whether high resolution audio is audibly superior to CD.

First, a little orientation. A standard redbook CD stores music encoded as 16-bit PCM (Pulse Code Modulation) sampled at 44,100 Hz. This standard was first published in 1980 and the first production CD player appeared in 1982.

Technology has moved on a long way since then, and around 10 years ago there was an industry format war over what higher resolution disc should replace CD. Sony championed SACD, which uses Direct Stream Digital, a 1-bit system with samples at 2822.4 kHz. Meridian and the DVD forum supported DVD Audio, offering a variety of possible formats up to 24-bit PCM sampled at 192 kHz.

Bigger numbers, better quality, right?

The 16/44 transparency test

Maybe, maybe not. Some audio engineers maintained that even 16/44 was more than adequate to convey audio with an accuracy greater than the limits of human hearing, at normal listening levels. In 2007, Brad Meyer and David Moran put this theory to the test. They conducted a series of listening experiments using high-resolution sources, testing one simple proposition: if you convert the audio signal to 16/44 digital and back during playback, is the difference in quality detectable?

Meyer and Moran wrote up their results in a paper published by the Journal of the Audio Engineering Society. Unfortunately the full paper is only available to AES members, but the results are well known and widely discussed. Their tests, which used double-blind testing techniques where neither listener nor tester knew which signal was being played, showed that no listener could reliably detect when the additional 16/44 conversion was inserted into the signal path.

On the face of it, this shows that no matter how good a stereo SACD or DVDA disc sounds, it could also be encoded onto a CD and sound the same to human ears. There was an unimportant caveat. If the volume was whacked up to very high levels, you could hear a difference in the noise floor.

What the transparency test does not prove

It’s worth noting that the Meyer/Moran test only covers one point: that 16/44 is (or is not) acoustically transparent. It does not prove that high-resolution audio is pointless; in fact, it has obvious value in production (as opposed to delivery), since production means digital processing, which degrades the sound; it makes sense to work in a resolution much better than you need for final output. I guess the same argument can be applied even to the distribution format, if the player is processing the sound to apply equalisation or bass management, for example.

Even if the test result is correct, it may still be that SACDs sound better than the same music on CDs, maybe because it is mastered better, or the player performs better with SACD, or maybe better source tapes were used for the SACD. In fact, Brad Meyer says:

Those who have read the JAES paper written by me and David Moran may remember that we too thought that the high-bit recordings we heard sounded, as a class, really exceptionally good. Our experiment, however, made a very good case for the theory that the reason for this lies not in the extra bits but in the market niche these recordings occupy.

Your rant against what you call square-wave recordings (i.e. ones in which the dynamic range is very heavily compressed to make the average level higher, which is a common mastering practice) is one I quite agree with, but it too has nothing to do with the number of bits in the recording. Our experiment showed that those awful-sounding things could just as easily have been issued as SACDs — and conversely that the excellent sounds we heard from our test material could have been issued in 16/44.1 without audible degradation.

Here’s how I think it works. SACDs are issued to a tiny niche market that is known to use good to excellent equipment, and to be fanatically devoted to realistic timbres and dynamics. Because the big guys in the record companies don’t care at all about such a tiny niche and are financing these SACDs because it’s the modern thing and sort of prestigious (and the other companies are doing it), they leave the engineers and producers alone, and the latter just make the stuff sound good on their own studio monitors and good home systems, and send ’em on out there.

And guess what? If a skilled engineer has as his only goal making something sound good enough to show off to his colleagues, you’re gonna think it’s pretty damn good too.

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