A useful test CD has recently come my way, courtesy of the Stereophile
editorial staff in Santa Fe (a copy was provided to each of the contributing equipment editors). Digital Test
was produced in France by Pierre Verany (PV.788031/788032, 2 CDs), and is distributed in the USA by Harmonia Mundi. It provides a wide variety of tests and useful musical selections, but the subject of special interest here is its test bands for evaluation of laser-tracking and error-correction capability.
There are two interrelated parameters which, in the absence of drop-outs or information gapswe'll get to them shortlycan affect the ability of a player to track the CD "groove" (or "whorl," as the quaintly translated disc booklet calls it): linear "cutting velocity" and track pitch. The standards for the first establish a range of 1.2 to 1.4 meters/second (the rotation speed of the disc varies from 500 to 200rpm from the inside to the outside of the disc to maintain this linear velocity); for the second, the spacing between adjacent tracks, from 1.50 to 1.70 micrometers (µm).