Variable pitch expands groove spacing before loud low-frequency passages and contracts it during quiet sections to maximize playing time

The physical width of a vinyl groove is set by the amplitude being cut, and low-frequency content needs the widest excursions. Variable pitch dynamically adjusts the cutting head’s pitch (grooves per inch): wider spacing in anticipation of loud low-frequency passages, narrower during quiet sections. A preview system (a time-delayed copy of the source) lets the lathe respond to upcoming passages before they arrive, maximizing playing time without groove overlap.

Examples

Without variable pitch a loud kick could make one groove overlap the adjacent revolution; with it, the pitch widens just before the hit to provide the physical room.

Assessment

What is the purpose of variable pitch in vinyl mastering, and how does the preview system enable it?