Record Grooves
The average LP has about 1,500 feet (460 m) of groove on each side, or about a third of a mile. The tangential needle speed relative to the disc surface is approximately one mile per hour, on average. It travels fastest on the outside edge, unlike audio CDs, which change their speed of rotation to provide constant linear velocity (CLV). (By contrast, CDs play from the inner radius outward, the reverse of phonograph records.) This allows the lock groove effect used by The Beatles on Sgt Pepper's Lonely Hearts Club Band, on which the last track, "A Day in the Life", runs into a continuous loop that will repeat as long as the record player is on.
Thin, closely spaced spiral grooves that allowed for increased playing time on a 33⅓ rpm microgroove LP led to a tinny pre-echo warning of upcoming loud sounds. The cutting stylus unavoidably transferred some of the subsequent groove wall's impulse signal into the previous groove wall. It was discernible by some listeners throughout certain recordings but a quiet passage followed by a loud sound would allow anyone to hear a faint pre-echo of the loud sound occurring 1.8 seconds ahead of time. This problem could also appear as "post"-echo, with a tinny ghost of the sound arriving 1.8 seconds after its main impulse.
The RIAA equalization curve (used since 1954) de-emphasizes the bass notes during recording, allowing closer spacing of record grooves and hence more playing time. On playback, the turntable cartridge pre-amplifier reverses the RIAA curve to flatten out the frequencies again.