Vinyl mastering lathes all work in one of two ways; fixed pitch or variable pitch; Fixed pitch lathes accept one signal and rely on the operator to adjust the land between the grooves to ensure there are no intercuts (intercuts are groove collisions which can lead to jumps and noisy pressings). Lathes that cut using Variable pitch accept two signals, one in advance of the other. The advance signal is sent to the pitch control computer and acts as a lookahead, which allows the lathe to know what is coming next and automatically adjust the land between the grooves.
This is far more accurate and responsive than adjusting it by hand, and can lead to louder and longer cuts as the grooves are packed onto the disc in the most optimal fashion. The Neumann VMS-80 cutting lathes that we use at Alchemy contain the most advance vinyl pitch control computers ever designed, for the most accurate groove packing.
When starting with a digital source it is easy to create a second advance signal to send through to the lathe, but when starting with an analogue tape source it is much more difficult, and requires a specially modified tape machine with two replay heads. Due to the scarcity of such machines, the vast majority of cutting houses that cut variable pitch masters will actually take the analogue signal into the digital domain in order to create the advance signal, and then back out into analogue to send to the lathe.
This requires two unnecessary conversions which degrade the audio signal.
At Alchemy our modified Studer A-80 preview machine not only gives us the ability to cut variable pitch with a pure all analogue signal path, but has modified Decca style ultra low noise replay amps for even greater audio fidelity, and both a ¼” and a ½” head block assembly.
Allied to this we have a range of analogue processors to enhance and control the audio before it passes through to the lathe, including the legendary Sontec MES – 430 B mastering equaliser (designed by Burgess Macneil and George Massenburg) and featuring a dual signal path specifically designed for pure analogue disc cutting, custom built dual path analogue stereo image control and elliptical equaliser, and a selection of Maselec, Dangerous and Gyraf analogue audio processors.