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In Reply to: RE: High Resolution - Fact posted by b.l.zeebub on April 09, 2014 at 10:50:01
The preview head does use a digitized signal but has nothing at all to do with the signal chain driving the cutterhead.
The idea is you take the output of the preview head (which is an additional tape head on the tape deck, about 2 seconds ahead of the main playback head) and create a digital output from it.
This output is then used to drive the electronics that operate the thread drive motor which advances the cutterhead across the LP. In this way, if there is a loud sound like a bass drum whack, the cutterhead makes room for it one rotation in advance so that the resulting groove will not overcut a previous groove.
This technology has indeed been around for a while and is known as 'variable groove spacing' or the like. The RCA Dynagroove system was an early analog version of the same idea.
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Here is what a mastering/cutting engineer has to say on this (they modified their lathe to get a true analog path):
"Marino describes, “The basic setup for cutting records is that you have an analog playback machine and the playback head feeds the signal to the cutting lathe. To cut a record properly, the computer in the cutting lathe needs to have a ‘preview’ [of what’s coming next as it’s printing], which is typically done via digital delay. The lathe gets two signals — the preview and the digitally delayed signal — and it’s the delayed signal that gets cut to the lacquer, which is not ideal.” "
Below link to article.
-And the better operations (RTI, QRP are examples) don't do it that way as mentioned in the article- they maintain an entirely analog signal path to the head.
There is no good reason I can think of to delay the signal in the digital domain, not if you are coming off of analog tape (unless you just don't want to pay for the machine work to do the preview head-nest). If the master file is digital then that is a different story.
We solved the problem by using an computer to store advance information of the LP side. So we have to play the source for it without the lathe running. Then we start over again, only this time the information gathered by the computer is used to drive the advance threads.
BTW Chris at Sterling is a customer of ours.
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