Half speed master

Thanks for the great explanation.

My understanding is that half-speed mastering was used to cut discrete 4 channel disc in the early 70s. It was developed so they could accurately cut 40kHz+ signals to the vinyl. It was thought that when used on normal stereo recordings that greater fidelity would be achieved, but there is some controversy over that claim. As a process it has stood the test of time, but in and of itself half-speed mastering doesn't guarantee better quality anymore than any other "remastered" claim.

Half-speed mastering is done to move the resonant frequency of the cutterhead up one octave. This makes it a lot easier to deal with. Decca developed this technique in the 1950s; many Londons and Deccas are 1/2 speed mastered.

The first answer was the right one:

Half-speed" mastering refers to slowing the cutting lathe to half-speed while cutting the album stamper. This resulted in a more accurate and deeply etched groove that improved bass response and produced more dynamic sonics.

This topic has been discussed at great lengths in Vinylengine.com. According to a Warner Bros mastering engineer who is a member out there, half-speed mastering is merely a marketing gimmick. It sounds nice only because a lot of care has been taken to master the record. Half speed mastering was required to overcome the limitations of record cutting styluses at that time. Post the 70's however, with helium cooling technology (I think), cutting stylus can cut at very high frequencies beyond 20khz.