12" 45 RPM records: What's the story?

Nsgarch, the preecho is in the other channel in the groove that has already been cut. The cutter cannot deform the vinyl in the groove yet to be cut.

What I would really like to know is how I get preecho on cds which are cut from the master tapes.

Tbg...You are correct about disturbance of the subsequent groove. Even if the recording media were upset by the cutter it would be "overwritten" when the cutter came by.

As for CDs with pre-echo, name one.

If the original source is analogue tape, the tape can have print through that will sound like pre-echo in any subsequent playback media.

So far, no one has explained just how this "pre echo" signal could be subsequently produced by deformation of the uncut vinyl, into a groove just cut, and "superimposed" on that already-cut groove with the ACCURACY of an actual cut groove, necessary to be able to identify the resulting signal (traced by the stylus,) as not only containing some kind of an "echo", but having the fidelity necessary to identify the original music signal that gave rise to it.

As for CDs, I agree with eldartford, never heard even an AAD CD with a tape print-through signal between tracks.
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Rushton...Master tape print through at the start of a selection is easily edited out when the LP is cut, or the CD data file is made. Also, FWIW, print through happens when tapes are tightly wound and stored unplayed for years. Also, newer tape formulations have minimized the problem.