Cutting Faster Than Real-Time? (100 rpm)

[cllw]

Hi Everyone,

I've been lurking this forum for quite awhile and realized I should sign up and contribute. I'm a master's student studying advanced product design working on a project related to home record cutting/DIY manufacturing.

I have question about theoretically cutting faster than real-time. I had an idea about how this could possibly be accomplished, but I'm sure it can't be this easy:

Speed up platter to 100 RPM (33 1/3 x 3)
Speed up source audio 300% without correcting pitch
Cut 18 minute album side in 6 minutes
Playback on standard turntable at 33 1/3 rpm

I believe this is basically the opposite principle of half-speed mastering? From what I have read, the theoretical HF limit for vinyl is around 70 kHz - the bigger issue is burning up the cutter head/coils due to the high speed/high frequency movement? I read that CD4 quadraphonic records had HF content up to 45 kHz, but they were cut at half-speed to allow for this?

I'm certainly no expert on the subject, just trying to learn as much as I can, and would greatly appreciate any feedback or criticism or other ideas on this topic. Thanks!

[markrob]

Hi,

The issue is the head not the vinyl. You will need to design a cutter head that has response to 60Khz. Good luck with that!

Mark

[Steve E.]

Not to mention the presumed effect of increased friction of the spinning acetate against the cutting stylus; though, of course, 78 rpm isn't all that slower than 100 rpm, I suppose, and that is done. There were even 100 rpm records back in the early, experimental days. (Though probably not in the 1930s dawn-of-acetate days).

[opcode66]

100 rpm with microgroove stylus would likely chip the tip.

[cllw]

Thanks so much for the responses so far.

IF a cutter head with response up to 60 kHz was attainable, is the basic premise of the concept reasonable?

Would cutting at 3x speed (100 rpm) and then playing back the resulting record at 33 rpm on a standard turntable, with an "average" stylus yield a similar end product to a record cut at 33 rpm?

Thanks again everyone!

[opcode66]

You are making the assumption that a stylus that is sized between standard and micro would be functional for cutting at 100 rpm. There is no easily accessible data to know this. Some similar things have been done with cutting early digital discs with diamond, but the groove geometry was different, and it was just making blips. Cutting constant grooves with lateral and vertical excursion poses different types of stresses on the tip than high speed digital cutting did. There just isn't a source of data to know what would be appropriate. Which means you would have to spend a lot of money out of pocket to perform the R&D to get that right.

Let's say you do however figure that out. By changing the size of the groove, you would require an "average" playback stylus. Using a playback stylus made for microgroove recording on a record cut in the way you are suggesting would have excessive noise on playback. A modern playback stylus would be dragging along the bottom of your "average" groove. That would require you to make and distribute your own playback styli.

The question really is, why? Is this a curiosity? Or, are you trying to figure out a way to speed up doing lathe cuts? You do realize that if you did get this to work and made your own playback styli to sit properly in your wider grooves you would have several unintended outcomes:

1. Recording at high speed is likely going to be lower sound fidelity. Due to some natural errors in physical systems, going faster will lose more data. Cutting slower supposedly would be more accurate though the lower octave of data would be lost. We've discussed half speed cutting on the site at length.

2. You would be giving up a significant amount of recording time due to unnecessarily wide grooves.

3. You would most assuredly wear out your cutting stylus much faster.

The last point to be reiterated is what Mark said. There may have been one experimental cutterhead at a university 40 - 50 years ago that could cut a 60K signal. One. You'll never find it. You'll never find someone today that could make you the equivalent. Sorry.

[THEVICTROLAGUY]

here is a path'e vertical cut center start disc playing at 100 rpm, this is circa 1906. at this speed a 10" disc has less than 3 minutes playing time.

[markrob]

Hi,

One other point. You would have to cut the 60 Khz frequencies with the same excursion as would be required during playback at 20 Khz. That requires higher acceleration of the cutting stylus and therefore more power to the head. So not only must you get response to 60 Khz, but you must apply much more force at that frequency. That's a really tough problem to overcome. High speed tape duplication was done back in the day, but there is no mass to move during the recording process.

The RCA CED videodisk spun at 450 RPM and had to be cut with very high frequency FM video information. They were cut at half speed (still 225 RPM). But the head was very different than the typical disk cutterhead (it was piezo based). It was also cutting very small excursions. In fact, this technology eventually became the basis for DMM. RCA spent a fortune on the process and it was dropped. Here is a link to a web site devoted to the technology

http://www.cedmagic.com/disc-manufacturing/05-master-lathe.html

So, if you really really want to do this, I would look into all of the RCA patents related to the CED.

Mark

[Greg Reierson]

The Lyrec moter in my VMS70 has a 66 2/3 winding. I imagine it's for voice recording or ???

[diamone]

There may have been one experimental cutterhead at a university 40 - 50 years ago that could cut a 60K signal. One. You'll never find it. And you'll never find someone today that could make you the equivalent. Sorry.

And if you do I have dibs so I can use it to cut DMM CD-4 real time mastering for 45 playback since I can't find anybody that could re-create the ortofon CD-4 real-time cutter head either - and there was SIX of THOSE instead of ONE.

...CED...

And Greg Bogantz could probably help you with all the CED patents.

The Lyrec moter in my VMS70 has a 66 2/3 winding. I imagine it's for voice recording or ???

16 RPM talking books for the blind were still being cut onto 12-inch (for 10-inch discs) and 14-inch (for 12-inch discs) because engineers didn't want to sit there for hours and hours cutting at 16 or 33 - same as they did once the speed dropped to 8-1/3 and everybody mastered at 33.

RCA Dynagroove tried it already back in the 60's cutting at 66 2/3 RPM just like they tried imposing an inverse pre-distortion curve upon mastering so that it would come out flat on the average phonograph of the period. Both experiments were COLOSSAL failures.