- Direct Metal Mastering
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Direct Metal Mastering is a vinyl record manufacturing technology by TELDEC. Records manufactured with this technology are often marked by a "DMM" logo on the outer record sleeve.
The cutting lathe for DMM engraves the audio signal directly onto a copper-plated master disc, instead of engraving the groove into a lacquer-coated aluminum disc. Examination of early DMM discs revealed what appeared to be a high frequency modulation in the groove, thought to be caused by the use of an ultrasonic carrier tone. In fact, there was no carrier tone and the modulation was simply caused by the vibration (squeal) of the cutter head as it was dragged through the copper disc.
There is one drawback of this approach and that is because of the modulation arising from this cutting method, criticisms have arisen of the sound of such 'DMM' records. They are often labelled as bright or edgy.
The Direct Metal Mastering technology addresses the lacquer mastering technology's issue of pre-echoes during record play, caused by the cutting stylus unintentionally transferring some of the subsequent groove wall's impulse signal into the previous groove wall. In particular, a quiet passage followed by a loud sound often clearly revealed a faint pre-echo of the loud sound occurring 1.8 seconds ahead of time (the duration of one revolution at 33 rpm). This problem could also appear as post-echo, 1.8 seconds after a peak in volume.
Another improvement is noise reduction. The lacquer mastering method bears a higher risk of adding unwanted random noise to the recording, caused by the enclosure of small dust particles when spraying the silvering on the lacquer master, which is the necessary first step of the electroplating process for reproduction of the master disc. As the DMM master disc is already made of metal (copper), this step is not required, and its faults are avoided.
See also
Production of gramophone records
References
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