As We See It

Sidebar 1: Error Correction

Most audiophiles still do not understand that error correction is not a Band-Aid for patching together a damaged signal, but is in fact the recovery of a perfect signal. Digital recording systems simultaneously use several systems for checking for lost or erroneous data and for completely correcting what's lost. The result is not "an educated guess" at the missing data, but a full reconstruction of it, identical in every detail to the original data. Listeners who claim to be able to hear error correction taking place are deluding themselves; corrected errors are 100% perfect. The "educated-guess" phase—referred to as concealment or extrapolation—is not invoked unless the correction phase fails, and it is very likely that concealment, which can rarely be 100% effective, will be audible if it lasts for more than a few milliseconds. But again, there is a mounting body of evidence indicating that most reports of its audibility result from a combination of suggestion (expectation) and self-deception (it isn't happening when it is claimed to be audible).—J. Gordon Holt

---

Footnote 1: Ah, but JGH: what about the oversampling A/D systems lurking in the wings? A 4x-oversampling A/D converter running at 176kHz will benefit from a much better-behaved anti-aliasing filter, possibly operating in conjunction with one in the digital domain.—John Atkinson