The technique of varying the groove spacing in relation to displacement amplitude of the cutting stylus.
"Just a note to say GREAT JOB putting my 2 lp's on cd. Both were old and both had some serious damage. I hardly even notice the parts where the damage was. Neither record was replaceable, and I figured it was hopeless; but you made them both enjoyable again. I can't thank you enough. Again, GREAT JOB"