Half speed mastering is a process in which the master for the pressing die, the so-called lacquer of an LP, is produced at half speed. Both the tape and the matrix move at half the playback speed. For records with a playback speed of 33 1/3 revolutions per minute (RPM), the speed for cutting the lacquer is therefore 16 2/3 RPM. In this way, the mechanical cutting stylus has twice as much time to carve the sound information into the matrix.
Cutting a lacquer is a very complicated electromechanical process: control signals for the cutting graver are generated from the electronic sound information of the master tape. These are amplified and passed on to the electromechanics of the cutting stylus.
Half the speed – twice the time
Mastering at half cutting speed – hence the name Half Speed Mastering – gives the graver more time to reach maximum deflection. At the same time, of course, the tape also runs at half speed. This increases the precision when transferring the sound information to the pressing die. As a result, the frequency response improves, there is less distortion, better transient response and greater dynamics.
The mastering process for half speed mastered records takes at least twice as much time as normal mastering at normal speed. In order to master as many LPs in the same time, twice as many studios, engineers and equipment are needed. This is why LPs produced that way are usually more expensive than conventionally produced pressings. Audiophile labels such as Mobile Fidelity Sound Lab, Impex or Analogue Productions rely on this method. But the famous Abbey Road Studios in London also employ experts for the process. There, for example, the various reissues of the Beatles catalogue have all been mastered at half speed since 2012. Just like the current reissue series of the Rolling Stones, Bob Marley or The Police.
Half Speed Mastering in the Abbey Road Studios
Half Speed Mastering has been around for a long time
Decca Records used half-speed mastering as early as the 1950s for the production of classic albums. The US soul label Tamla Motown, which was famous for the powerful sound of its records, is also said to have cut their laquers at half speed as early as the 1960s.