Amazing samples found here.

"To re-time the audio signal, the special Clarity transfer equipment recovers signals in the ultrasonic region that can be found on the tape or film along with the audio of the original recording. By ascribing to these ultrasonic components the properties of a moving clock (think varying sample rate), and mathematically retiming these signals such that the clock is crystal-steady, the dsp now “knows” the speed fluctuations of the original machine occurring at the moment it made the recording. By inverting the error signal, and conforming the corresponding audio to it, Clarity’s dsp retimes the audio to a fixed and stable time base. The result: perfectly pitched audio with no wow or flutter."

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I came across this a while ago too -- it's fascinating stuff. Seems to me though that if 'ultrasonic' signals are being used, that means that any digital archiving for later 'Clarity' treatment *has* to use sample rate such that the nyquist frequency is double or more that ultrasonic frequency. Meaning, if the ultrasonic signal is >22kHz, you can't 'Clarify' a Redbook recording that way.