Harryup skrev:Varför skulle man vilja ha en Shibata-slipning? Den tillkom som ett nödvändigt ont för att spela av bakkanalerna i CD-4. Inget sliperi kunde vid tidpunkten slipa några micro-ridge i 3D utan man kunde bara lägga in ett plan på en rund nål. 
Vilket får till följd att vid övergång mellan 2D planet i bakkanten mot den runda 3D ytan så blir det en böjd kant. Den kommer att medföra att nålen rör sig i höjdled i spåret och sliter därmed ganska mycket mer än nödvändigt på skivorna. Förmodligen vore det bättre att nålen satt åt andra hållet eftersom spåret ju träffar nålen i bakkant.
Jag refererar till dem som var med då det begav sig så kanske det klarnar, de verkar ha en lite annan syn på varför:
When they developed CD4 Quad 4 channel recordings, they needed to be able to record and play back frequencies up to 45kHz - more than twice the highest goal frequency attained with the elliptical styli.
Also the very fine corrugations in the groove required for 45kHz could be more easily worn away, so a design was required that could 1) track much higher frequencies and 2) Reduce wear on the record.
The first stylus that achieved this was the now famous "Shibata" (named after its inventor).
Elliptical and Shibata Stylus showing contact patch
Proportions of the Shibata design
6 x 75 um - Shibata "large" design
6 x 50 um - Shibata "small" design
Rather than providing a small circular "dot" contact point with the groove, the more complex shape of the Shibata allowed a long vertical line of contact to be achieved with the groove wall.
The result of contacting more of the groove wall was the achievement of the two primary goals.
Through better wall contact tracking was improved and information retrieval improved (facilitating higher frequencies), and because the total contact surface area increased, the amount of pressure per square area was substantially reduced - less pressure equals less wear on both the record and the stylus.
In actual fact the side radius of the Shibata is about the same as a 0.2 mil elliptical - so theoretically they have the same ability to trace high frequencies, but the elliptical only ever contacts the same small area - which can become worn - resulting in degradation in high frequencies.
Playing back a record with a Shibata stylus which has been worn with a conical or elliptical stylus can result in near pristine sound - this is because the Shibata shape can "read" the groove wall in areas that were not contacted by the simpler stylus shapes.
After the release of the Shibata, various competitors developed very similar shapes which were (and are) marketed under various names:
Hyper Elliptical (various sizes!)
Stereohedron 0.3 x 2.8 mil / 7 x 72 um
Line Contact  (various sizes)
Fine Line         8 x 40 um
These are all much the same