faint precession of sound on vinyl

Shadone...I am a professional musician and can tell you flat out that pre-echo should not be there. It is not natural and is sometimes a serious fault. I believe this is from the storage of the tape when a the adjacent layer picks up the magnetic energy from its neighbor. Usually it can be heard during a quiet passage just before a louder one. I have heard pre=echo on a CD version of an older performance as well.

Stringreen: I thought so. It is the only plausible scenario I have heard yet. I have heard so many weird explanations ranging from satanic conspiracies to the aforementioned theory of engineers adding 'richness'. I listen to so much quiet music that it can be a problem, however there is no substitute for vinyl, IMO.

Actually, you are totally right. I checked out and I heard it on an older recording of a Bach cantata on CD. It is not a vinyl thing after all. I guess much of the time they eliminate it from the master tape when they make a digital transfer, thus it is less frequent on CD.

I can pull out a dozen CDs that have pre-echo. It's the master tape, not the format.

It is almost always groove-to-groove interference. This is easily verified by timing the amount of pre-echo. If it's 1.8 seconds it is a LP problem. Mag tape print-through is also real, but usually requires storage of the tape for years without rewind, and the timing will vary with tape speed and how much tape remains on the reel.

Pre-echo can be eliminated by wide groove spacing, but that drasticly reduces playing time. So groove spacing is dynamically varied as the record is cut according to the music signal amplitude. As always there is a compromise, and the grooves are kept as close together as possible, accepting a small amount of pre-echo that only audiophiles will complain about.