The master recording lathe receives a frequency modulated signal from the master control unit in 1/2 real time. The diamond cutter on the lathe vibrates up and down three million times per second as it cuts the groove in the surface of the copper master.

The electromechanical recording lathe shown above was designed and built by Gunter John in Indianapolis. As Jerry Halter perfected his cutterhead on a modified Neumann record lathe, Gunter incorporated an air-bearing spindle and cross-slide to precisely control the translation and rotation of the copper disc into which the groove and modulation were cut. This design permitted RCA to expand capacity and license the technology to CBS.
- James E. Lang

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