Direct Metal Mastering

Direct metal mastering (DMM) is an analog audio disk mastering technique jointly developed by two German companies, Telefunken-Decca (Teldec) and Georg Neumann GmbH, towards the end of the 20th century after having seen the same technology used by RCA Princeton Labs for their SelectaVision videodiscs in the late-1970s.

Records manufactured with this technology are often marked by a "DMM" logo on the outer record sleeve. Many current production high quality pressings, as well as standard production LPs from the 1990's, only indicate its use by inscribing "DMM" in the lead-out groove area of the disc.

Neumann was responsible for manufacturing the actual DMM cutting equipment as part of their VMS80 series lathes. Unlike conventional disc mastering, where the mechanical audio modulation is cut onto a lacquer-coated aluminum disc, DMM cuts straight into metal (copper), utilizing a high frequency carrier system and specialized diamond styli, vibrating at more than 40 kHz (i.e. 60 kHz) to facilitate the cutting.

The advantages of DMM (hard surface material) over acetate lacquer cutting (soft surface material) are both sonic and practical: because of the rigidity of the master disc medium, no groove wall bounce-back effects take place after the cutting has been completed. This preserves the original modulation details in the groove walls much better, especially those involved with sudden fast attacks (transients). The improved transient response, as well as the more linear phase response of DMM improve the overall stability and depth-of-field in the stereo image. In addition, disturbing adjacent groove print-through sounds (groove echoes) are reduced in DMM. Also, there is no need to rush the finalized master disc directly into a refrigerator for groove preservation, as in conventional lacquer disc cutting, before processing the master disc to produce matrices for the pressing of the records.

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