Saturday, February 25, 2012

A correction on correction

Rev A (see Notes)

Because I ran into some evidence that seems to disprove my assumption that the optical-disc correction system is far from perfect, I looked into the issue some more, and found The Numerically-Identical CD Mystery: A Study in Perception versus Measurement, which indicates that the problems which I was attributing to poor "on the fly" error correction are more likely caused by perturbations in the disc-player's power supply as the laser-servo mechanisms work to keep the laser focused on the right track.  These perturbations then subtly modulate the output signal, producing effects which critical listeners hear.  The study indicates that this problem is not noticed in "two box" players, which makes sense.  It would also explain the lack of such effects in computer audio systems with well-designed separate DACs, and in systems in which flash memory is the source.

So, this would indicate that for the ultimate fidelity at a reasonable price, SACDs are the way to go, but that the optical drive's power supplies need to be completely isolated from the rest of the power supplies.  It also undermines the case for spending thousands of dollars on a precision transport.

As evidence that transports don't actually make a difference,  unless their jitter is so bad that it causes bit errors (although eliminating as much jitter as possible is critical at the DAC clock inputs), I cite an experiment  in which an audiophile compared a dirt cheap CD player with digital outputs, used as a transport, with his supposedly highly superior Arcam transport.  He indicates that he heard no difference.

Commercial audio reviewers have a vested interest in claiming that transports sound different, and this is that their job is to sell as much expensive gear as possible to rich people.  This fixation on transports is a holdover from analog turntables, which do indeed generally sound better as price increases, at least at this point in their development.  It's not unusual for wealthy audiophiles to spend $10K-20K on a turntable system, and the most expensive is in the neighborhood of $300K. They might even sound better than a $1500 SACD player playing a recording made with a Grimm AD-1 analog-to-DSD converter.

Notes
Rev A: Added last two paragraphs