This is an excellent and informative article. I am a fan of Keith's writing. What we all must remember is that the data on a disc do not trace out the waveform at higher frequencies. The data points on the disk are the skeleton for the digital filter to flesh out. His point about the ringing pattern of the digital filters time domain response being directly responsible for replicating the higher frequency components of the waveform is one that many detractors of digital audio seem to be unaware. It is pretty close to magic that the algebraic sum of all the ringing patterns should end up replicating the waveform so completely, yet that is exactly (nearly) what happens. It should be noted that J. Peter Moncrief (IAR) made exactly the same point back in about 1989 in his review of the first Theta Digital DSP(and custom, advanced reconstruction algorithm)-based D/A converter. It also makes me question the validity of designs that use no digital filter (47 Labs, Zanden). Note: if I understand correctly, the Wadia has no ringing of a single sample, but uses a different algorithm, based on multiple samples, to reconstruct the high frequencies, i.e. it definitely has a sophisticated digital filter.
Anyway, very interesting reading Mr. Howard. I don't mind having my brain twisted, so keep asking the intersting questions!