DIY half speed mastering?

[oldsyd]

Has anyone here tried mastering vinyl by playing it back at half speed and then correcting the speed in digital format?

I thought of it going through some of my old vinyl seeing the records which were cut at half speed deemed "audiophile"

It makes sense the slower you go, the more accurate the tracking would be.

 

[winopener]

Yes, and haven't found a way to get rid of the extra rumble without killing badly the sound.

 

[ndiamone]

A Studer-Revox linear tracking does pretty good for recording OMR's and HSM's and Nautilus into the computer. Either find one on eBay or wherever that's already been converted, do the quartz lock speed conversion by yourself, or take it in to an audio salon and have them do it.

The other one that works is the Technics turntable I think it's an S-10 or X-10 I forget that comes without a tonearm or a place to put one. It does however come with a place to install an overhead carriage linear tracking tonearm, which you can also get.

Try and find linear tonearms with the optical scanners in. These correct for the varying pitch as the stylus gets to that part of the record by scanning the grooves ahead of the stylus and driving a lead screw onto which the tonearm carriage is affixed. With the scanners, it anticipates where the stylus needs to be when, and speeds up or slows down the tracking motor driving the lead screw right on time, just as a recording lathe pitch control would when originally cutting the master.

IMHO since in the normal two-magnet style of linear tracking, the stylus follows the groove and then an instant later, the magnets line the cartridge back up to the groove portion, the playback always has imaging and other problems. This is because it's tracking corrections are always late, technically leaving the stylus slightly cockeyed most of the time as it's continuously doing it's after-the-fact corrections.

To get rid of the minimal rumble that remains, place a Sorbothane mat onto the turntable under the record in place of its' original slip mat, as well as Sorbothane feet under the turntable itself. Your standard semiconductor Shibata setup or any other good cartridge and stylus should work fine after that.

Or you could just wait for Carl Haber to finish perfecting his disc and cylinder scanner http://www-cdf.lbl.gov/~av/LBL-RPM-V4-nI.pdf at the Lawrence Berkeley Labs, and then go buy one of his Virtual Turntables once they are perfected. Then you wouldn't have any turnover issues, tracking issues, preamp sound-coloring issues, cartridge or stylus issues, groove-size issues or anything else.

 

[proufo]

Has anyone here tried mastering vinyl by playing it back at half speed and then correcting the speed in digital format?

I thought of it going through some of my old vinyl seeing the records which were cut at half speed deemed "audiophile"

It makes sense the slower you go, the more accurate the tracking would be.

A least one member has tried it with CD-4 records.

RIAA is an issue. You would need to record them without RIAA and apply it in the digital domain or do something more complicate.

I still have such project in my back burner.

 

[ndiamone]

You would need to record (into the computer) without RIAA and apply it in the digital domain...

Diamond Cut Pro is about the only decent RIAA (or other turnover) curve available in the digital domain without doing it yourself by hand. Same is true for the digital demodulation of CD-4, that is if you choose to use the 13.75MHz sample rate normally intended for uncompressed video so that the digital software demodulator has enough carrier wave samples off which to demodulate.

That's if Dorren's demodulator won't demodulate 15 KHz instead of 30, or have a switch for no RIAA turnover, which maybe it will and maybe it won't.

 

[oldsyd]

Very interesting stuff. Unfortunately it's much more difficult than I thought.

I think I recall some sort of optical scanner method used for playing back the oldest audio recordings from a phonautograph not too long ago.

 

[Dylan Berichon]

Diamond Cut Pro is about the only decent RIAA (or other turnover) curve available in the digital domain without doing it yourself by hand. Same is true for the digital demodulation of CD-4, that is if you choose to use the 13.75MHz sample rate normally intended for uncompressed video so that the digital software demodulator has enough carrier wave samples off which to demodulate.

That's if Dorren's demodulator won't demodulate 15 KHz instead of 30, or have a switch for no RIAA turnover, which maybe it will and maybe it won't.

Diamond Cut's tools are the best I've ever used, for what it's worth.

Those guys really know what they are doing.

 

[Lucanu]

Will a optical digital turntable playing half-speed do the job?

 

[ndiamone]

Very interesting stuff...optical scanner method used for playing back the oldest audio recordings from a phonautograph...

If you mean http://www.retrothing.com/2008/03/the-phonoautogr.html then it's the same people as Carl Haber and his optical Virtual Turntable discussed above.

They turned the (rag) paper (upon which the phonautographed recording was inscribed in lampblack) over to scientists (such as Carl Haber) at the Lawrence Berkeley lab who retrieved the sound with the help of modified software (and hardware) that was originally intended to play high-resolution maps of grooved records. The result is an eerie fragment of song by an anonymous vocalist: Au Clair de la Lune.

Will a optical digital turntable playing half-speed do the job?

If you mean the quasi-experimental versions of the optical turntable that have been around since the start of the New Millennium, I believe on the ones I've seen, they don't feature 78 or 16 speed, hence no need for weird turnover curves. IIRC these turntables feature Line Out, not Mag-Level-Out with no turnover.

And then, they also cannot play colored records, either the transparent ones, or a lot of opaque ones either like Quiex or Nautilus. They also skip a lot, but at least the skipping does no harm to the record, and it takes a lot of takes before you can re-cord a rec-ord completely into the computer from there, at least on the ones we auditioned a few years ago.

Maybe there's better ones out now, but they'd still be extremely expensive, as niche-market as they are.

 

[oldsyd]

Just to make sure, there's two different types of optical technology here:

1. The scanning technology that ndiamone mentioned, which isn't really
a turntable, but a process of scanning the record surface and then using software to read the grooves on the recording.

2. The Laser Turntable, which uses a laser to read a spinning disc similar to a stylus.

I know ELP says #2 will not read colored or transparent discs, but I'm not sure about #1. I would think a flatbed scanner could see the detail in a colored or clear groove, especially if it was lit correctly. Process #1 doesn't need to rotate the disc to scan it, unless it's a wax cylinder.