As the record spins, the stylus (needle) rides in the groove. The groove walls push it around; that motion travels through the cantilever into the cartridge, which generates a tiny electrical signal.
Both convert motion into voltage, but they differ in output level, typical cost, and what preamp they need.
The stylus must stay in contact with the groove while moving extremely fast at high frequencies.
Key idea: playback quality is often limited by whether the stylus can faithfully follow the groove’s fastest, smallest details.
Why do very high frequencies tend to be the first thing to sound distorted when a stylus is mistracking?
When the groove changes direction rapidly, the stylus has to accelerate quickly to stay in contact; that’s mechanically demanding, so mistracking shows up there first. A common misconception is that treble is ‘deeper in the groove’ (dust can matter, but frequency isn’t mapped to depth like that). Another tempting idea is blaming the preamp for ‘creating’ treble—preamps shape and amplify signals, but the treble information is already in the groove motion. And stereo information isn’t assigned as ‘mostly left’ for high frequencies; both channels carry the full spectrum.