hIgh-speed cutting?

[marchingband]

Has anyone had any luck cutting 33rpm discs at 78? (And by that I mean cutting a disk at 78 that is intended for playback at 33, in order to save time)
If the program material has the RIAA filter applied, and is then pitched up by a factor of 2.36, it seems to me that it should work, but my results are very poor : severely attenuated lows, and a strange peak around 2k. The highs are also quite attenuated.

I searched the forum but couldn't see a thread that addresses this, so I thought it could be useful to discuss.

What am I missing !?

[grooveguy]

Hey, M.B.

What I think you are missing is that everything is being translated down by a factor of 2.35, the difference between 78 and 33-1/3 r.p.m. When you play the music faster, the cutterhead still has a 10-15kHz cutoff frequency, so when you play back at 33-1/3, your cutoff is 4.25kHz instead of 10kHz (assuming that your cutterhead is flat to 10kHz.) And even if the cutterhead is flat, the geometry of the cutting stylus was meant to deal with only certain wavelengths (expressed in thousands of an inch, not Hz), and they get translated down too. The lower frequencies really ought to profit from this conversion, but the equalization curves used for disc recording may not be friendly to this frequency translation technique.

Back in the 1960s when I was engaged in the development of high speed tape duplicating systems, we were using electrical bandwidths out to nearly 1MHz just to get flat response to 12kHz on 1-7/8ips cassettes. If the whole system is developed along these lines, you can accommodate the frequency translation. But especially with a mechanical recording system, you are at the mercy of mechanical resonances and wavelength situations. Nice idea, though: make your copies at 1000 r.p.m and do both sides of an LP in a minute and a half! (Actually this may not be all that far-fetched. The Teldec (mechanical) recording system for video discs in the 70s had to accommodate video frequencies, probably out to 3MHz or so. With a proper piezo or magnetostrictive cutterhead, you might be able to make very faint audio recordings at 100X... if the recording blank doesn't disintegrate!) See: http://www.cedmagic.com/history/teldec-1970.html

[dubcutter89]

I think grooveguy is right about high speed duplicating and the problems with mechanical systems...

side note on TED: I have seen pictures of the TED-cutters, and these were heavy modded VMS66 with special platter and cutter and the discs were cut at 1/25 speed (!) so a 10 minute video took over 2 hours to cut.
a main problem was the tape playback which had to be modded too - thay used hall sensors instead of regular heads to get the response down.

Lukas

[marchingband]

Thanks Grooveguy, that definitely makes sense.

[diamone]

The only two places I ever heard of high speed cutting was for magazines and talking books for the blind which were cut at 33 for 8 playback or 33/66 for 16 playback.

The other place I heard of it is when my uncle used to work at Mattel and they'd cut doll records at 133 for 33 playback.

Of course the reverse is also true - a great number of doll records were also half-speed mastered at either 45 for 90 playback or 78 for 156 playback for the really small discs that got maybe 15 or 30 seconds on a side.

And then if you have a two speed Scully for example and you set the ``33'' for 45 with a different diameter - then the ``78'' becomes 105 which was also done - real time for real time playback.