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Steve E.
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Avoiding grooves kissin' each other. Test frequencies!

Post: # 25595Unread post Steve E.
Fri May 24, 2013 10:40 am

So here's a fun thing I learned/co-figured-out yesterday, while conversing with Leo G. Maybe this is common knowledge among some of you, but it was news to this perpetual newbie.

Let's say you're in a situation requiring a given fixed-pitch LPI, and you want to know the maximum loudness you can use on some bass-heavy material without your grooves touching. You don't want to take chances.

Running a test signal at, say, 60 hz will not be helpful to you, because you can really pack grooves in like Pringles potato chips at that frequency, at both 33 1/3 and 45 rpm: [photo to come, but imagine ridiculously and misleadingly cozy grooves for now.] This is because, on each rotation of the turntable, the waves complete a full cycle.

If you are running your turntable at precisely 33 1/3, try test-cutting this bass frequency: 62.5 hz (or cycles per second). At one rotation of 1.8 seconds, the groove will oscillate precisely 112.5 times. So every new rotation will feature a groove precisely out of phase with the one before. You will get a cut demonstrating the "groove kissing" potential at any given volume.

Gradually bring up the level. Monitor the results using a microscope. The loudest level at which you can safely cut this frequency without the grooves kissing is also the approximate peak volume level of your program. When the level is too high, it will look like this: [awesomely patterned photo to come.]

This trick works with any frequency which, when multiplied by 1.8 seconds (= 1 turntable turn at 33.3), gives you a waves-per-rotation number ending in ".5" The REAL secret is, it works by taking any frequency which is a multiple of 5....and adding 2.5hz. so, 67.5, 72.5, 122.5 etc.

This is messier at 45 rpm. You are still looking for a frequency which, when multiplied by 4/3, will give you a number of waves-per-rotation ending in .5.

The REAL secret here is to take any frequency that is a multiple of three, and add to it 3/8 (=.375), or 9/8 (=1.125) , or 15/8 (=1.875), or 21/8 (=2.625).


So, for example:
60+ 21/8 = 60 + 2.625 = 62.625.
or,
87+9/8 = 87+1.125 = 88.125.

I'll leave it to someone else to figure out the numbers for the US and non-US versions of 78 RPM.

Again, this will only work if your turntable is turning at the precisely correct speed.

If YOU have any real world experiences or improvements on what is admittedly my mostly theoretical approach here, please add them to the thread!!

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EmAtChapterV
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Re: Avoiding grooves kissin' each other. Test frequencies!

Post: # 25644Unread post EmAtChapterV
Sun May 26, 2013 9:34 pm

For groove-kissing with regular music material, I used to keep an eye out for songs that were close to but not exactly a multiple of the record speed - around 100, 133 or 167 beats per minute, with very deep bass or a prominent kick drum in the mix. The resulting records would look more like an angry octopus rather than spokes on a wheel.

Two in particular I used to use back in the day were the break in Leaving Town by Chicane - http://www.youtube.com/watch?v=JMFFbVGPDwA&t=2m41s (Far From The Maddening Crowds, Edel Music/ Universal, 1997), and the beginning of Your Lucky Day In Hell by Eels - http://www.youtube.com/watch?v=jsMTudiRaSc&t=9s (Beautiful Freak, Dreamworks, 1996). Here To Stay by Korn was also a challenge - http://www.youtube.com/watch?v=ZCIcyKmJj5I (Untouchables, Epic, 2002)

Of course I have a Rek-o-Kut so speeds and thus results could vary by as much as 0.2%. I'd be interested to see how these examples would turn out on a Neumann with absolute rotational precision.

(Edit - geez, that Youtube video of Eels sounds like compressed a$$, but it was the only one I could find. Sorry. The proper CD recording sounds wonderful. Plus it has vibraphone as well as the kick drum for an extra challenge. Add some muted trumpet or a tambourine and it would be a full-frequency cutting fidelity test hat-trick.)

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EmAtChapterV
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Re: Avoiding grooves kissin' each other. Test frequencies!

Post: # 25645Unread post EmAtChapterV
Sun May 26, 2013 10:37 pm

Also, and please excuse the dust, here's a 300 Hz tone lateral and vertical trackability test on Hi-Fi Sound Stereo Test Record, HFS-75.
Dscg0019x.jpg
Note the frequency drift on the three outer (lateral) bands. The liner notes say this was cut direct from a frequency generator to an Ortofon DSS661 on a Neumann VMS70, so I wonder why what's supposed to be 300 Hz went from nestled (as it should be) to... decidedly not.
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flozki
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Re: Avoiding grooves kissin' each other. Test frequencies!

Post: # 25659Unread post flozki
Mon May 27, 2013 3:28 pm

we use for pitch calibration always:

Cutting Level: +6dB @ DIN 8cm/s or NAB 7cm/s peak reference
99.722Hz mono (for 33rpm)
30.278Hz mono (for 33rpm)
99.375Hz mono (for 45rpm)
30.375Hz mono (for 45rpm)

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Steve E.
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Re: Avoiding grooves kissin' each other. Test frequencies!

Post: # 25665Unread post Steve E.
Tue May 28, 2013 2:13 am

Nice! Thanks, Flo. And thanks, Em.

Why +6? Is that equivalent to momentary VU peaks at 0?

I know nothing about the DIN standard.

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EmAtChapterV
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Re: Avoiding grooves kissin' each other. Test frequencies!

Post: # 25683Unread post EmAtChapterV
Tue May 28, 2013 6:32 pm

+6 dB is the standard for twelve-inch dance club singles, which with normal program material and cutting parameters usually results in grooves kissing at around 105 to 110 lines per inch, maybe 95 to 100 under worst-case scenarios. Anything around +8 dB or higher runs a serious risk of unplayability with entry-level DJ cartridges like Ortofon Concorde. And unless you're cutting the 1812 Overture, it's unlikely you'd be fine-tuning your variable pitch settings for records that loud.

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audadvnc
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Re: Avoiding grooves kissin' each other. Test frequencies!

Post: # 26025Unread post audadvnc
Fri Jun 14, 2013 11:18 pm

How deep are you running your stylus at +6dB? With any significant out of phase LF material level you can expect to see your cutting needle flying out of the groove unless you set that stylus deep... I've ruined more than one side getting too enthusiastic with my levels, only to find the groove disappear in spots.

As for picking a frequency that generates most trouble? 20Hz has the most mono excursion by far on my Westrex system.

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