Super Audio CD: The Rich Report Postscript from December 2000
In the November Stereophile, David Rich raised some technical questions concerning the DSD encoding used in Sony's and Philips' Super Audio CD medium. Again, I had been puzzled. Basically, given its 1-bit format, the seventh-order noise-shaping employed, and the 64Fs (2.8224MHz) sampling rate, DSD should not be capable, in my opinion, of producing the increase in dynamic range and high-frequency extension claimed—nor, as Mr. Rich pointed out, should it be stable enough to do so without introducing spurious tones. Like Meridian's Bob Stuart in this issue's "Letters" (pp.9-10), David Rich came down firmly on the side of high-resolution Linear PCM. Yet not only does DSD appear to offer those dynamic-range and bandwidth benefits, it both sounds great and does not suffer from spurious tones.
As you can read in Barry Willis' report from the 109th AES Convention in this issue's "Industry Update" (p.22), respected audio theoreticians John Vanderkooy and Stanley Lipshitz shared David Rich's concerns about DSD. Perhaps not coincidentally, Sony has revealed that, while the DSD data on an SACD are still 1-bit-encoded, the encoding system actually uses a multibit quantizer, presumably within a digital negative feedback loop, as described by Mr. Rich. Mystery solved.—John Atkinson