Also, it's important to not assume that any given groove is
"vertical". As with all mechanical devices, tolerances are involved. IF
a groove induces a stylus to meaningfully oscillate at some angle other
than true perpendicular (+ or - the theoretical standard), then unnecesary
low and high frequency noises will occur. This is remedied by continually
adjusting the phase relationship of the stereo cartridge being used to
track the grooves. I call the process "vectoring". It's extremely
beneficial for ALL monaural grooves.