DAC Converters.

[opcode66]

For those who use a different DAC for Preview than they do for Program output I have a question.

How do you insure that the signal coming from both devices is the same intensity? From my experience, the output of different units vary given the same signal from a DAW.

If the Preview signal is weaker than the Program signal then you risk overcuts. If the Preview signal is more intense than the Program signal then you will be wasting spce (i.e. have way too much land).

How do you all compensate for that? Are you metering each device?

[gold]

How do you insure that the signal coming from both devices is the same intensity?

Calibrate both so X dBfs= X dBu. Usually with a 1K sine wave. Make sure to use a true RMS volt meter. You could check the frequency response but I've never run into a DAC that didn't have virtually flat frequency response.

[duomo]

you have to calibrate the input of your SV 66 cards anyway ( I have the old analog pitch). I used the pitch testtone form flo kaufman. There are 4 or 5 sinus tones so you are sure your pitch work exactly over the whole frequency range. I have also a eq in the preview channel to optimize the control unit , that helps a lot !!

[opcode66]

Thanks for the replies. I appreciate it. That's what I figured would be required.

I've not calibrated my input cards. I haven't read anything that describes that procedure. I'm guessing they were calibrated by Al. Anyone have information on calibrating the input cards?

I use a DAC with two stereo output pairs. So, my Preview and Program are coming from the same device. But, I plan to upgrade the Program output DAC. So, this information helps.

[dietrich10]

Many high end DAC will have internal output attenuators to adjust(my HEDD has on the back next to the outs + ins).

As long as you get Preview+mod with .25dBu should be gold

[habib]

i use a unique hand make David Manley Dac with aes and xlr to cutting amp sal 74b. Unique sound !!!

[Lex]

I use a Weiss DAC 1 for the signal to the Ortofon Amps and a Weiss ADC 1 - DAC 2 for the delayed preview signal of the VMS 80 and also for the VMS 70

Lex

www.thevinylroom.nl

[Dub Studio]

Cranesong for analogue inserts, and Crookwood for both monitoring and cutting. All running through Crookwood console. Personally I think going AES + DAC is way better than a soundcard solution, mainly for practicality, compatibility and versatility, and also sound quality for those who care about it.

[MrMegaEli]

check this out: http://www.diyrecordingequipment.com/1631/the-mcm-dac-mod-a-world-class-converter-for-under-150/

[Serif]

...

If the Preview signal is weaker than the Program signal then you risk overcuts. If the Preview signal is more intense than the Program signal then you will be wasting spce (i.e. have way too much land).

How do you all compensate for that? Are you metering each device?

I'd like to know how the VA66 handles this, but on the LS-76, it is recommended to use extra attenuators for the feed and depth computing pairs of signals so that they can be trimmed deliberately to be offset from their respective base pitch/base depth settings when a base pitch for a cut is selected which is different from that which was used to calibrate the system. For example, the base pitch to which the system is calibrated might be 400 LPI. But if you wanted to cut a long, quiet side at, say, 600 LPI, depending on program characteristics, one would have to attenuate one or both pairs of control signals (Advance Right/Program Left (for Feed) and Advance Right/Advance Left (for Depth)) in order properly to scale the voltages it sees in the audio to result in the efficient use of land. Otherwise, in spite of the low level of the Advance audio signals, which would ordinarily be the same as the level of the Program audio signals for this hypothetically long quiet side, the selected Base Pitch might never be realized (due to the deck never adequately de-expanding (\; ), resulting in wasted time/fidelity because the changes in the voltages in the lathe movement computer during the cut would goose the Feed up by the step size ramps which were calibrated to a base Pitch of 400 LPI. Similarly, if one wished to cut a loud or bass-filled side at, say, 250 LPI, unless one increases the level of the signals that go to the lathe movement computer (beyond the gain used for Program), overcuts, where groove walls touch more than a kiss, or even twining, where grooves overlap, may result if the system was calibrated at a higher LPI (e.g. 400 LPI) because of the scaling of its space-saving imagination. I know, it should be able to tell itself how to deal, but it was about 1976 by the time the first one was built, and there was so much Disco-going to be done... in Bridgeport. hehe....

How does the Neumann computer do the extra maths for the operator?

Do you use extra trimmers, shoot new tones, in and out of phase each time you change feed, or is that a set-it/forget-it deal even if you have different cuts at different BP?

- Andrew

[gold]

There are different ways to skin the cat. The SV66 can only offset about 6dB at 40hz so no setting will work for everything. If base pitch is set too tight you will get overcuts. Setting a base pitch of 600LPI is a recipe for disaster un;ess you do a lot of spoken word.

The controls on a VMS66/70 are LL, LV and V. Lateral offset as a result of lateral modulation, lateral offset as a result of vertical modulation and vertical offset as a result of vertical modulation. You could adjust these controls for offsets. I did that for a long while but have since mostly stopped doing that as I have other tricks now.

The Neumann consoles had preview offset controls. This is just a straight level control. I think the nicest way to do it is to have the preview offset sum/difference so you can control lateral and vertical separately.

I doubt you will be cutting sides at 600LPI.

[Serif]

There are different ways to skin the cat. The SV66 can only offset about 6dB at 40hz so no setting will work for everything. If base pitch is set too tight you will get overcuts. Setting a base pitch of 600LPI is a recipe for disaster un;ess you do a lot of spoken word.

The controls on a VMS66/70 are LL, LV and V. Lateral offset as a result of lateral modulation, lateral offset as a result of vertical modulation and vertical offset as a result of vertical modulation. You could adjust these controls for offsets. I did that for a long while but have since mostly stopped doing that as I have other tricks now.

The Neumann consoles had preview offset controls. This is just a straight level control. I think the nicest way to do it is to have the preview offset sum/difference so you can control lateral and vertical separately.

I doubt you will be cutting sides at 600LPI.

Hi Paul,
Agreed, even most Classical would be too forte and/or basso for 600 LPI to be a successful Base Pitch choice. Still, I can imagine odd scores involving long, quiet intros, such as that of Henryk Górecki or Holst requiring the use of a higher Base Pitch number than that which one has calibrated his LS-76 to... Alas, the magic numbers were for illustration of the sensitivity (i.e. lack thereof) of the overall computer and the need to spoon feed it in these atypical cases (or, conversely, to force it to beer bong the levels, as it were, in accordance with a much lower than normal selected Base Pitch).

Of course, it is a Base Pitch I am referring to, and not a Fixed Pitch. On board The Lathe is only Expansion and De-Expansion. Unfortunately, no Contraction beneath the Base Pitch will happen, so, a suitably high count for Base, if not for Count Basie, without being inappropriately high, is wanted for the specific program (How about cutting some silent symphonies by Dadaist Composers? (; .) Unlimited Contraction and Expansion would have made possible the avoidance of needing to recal with either tones or attenuators the way the lathe computing responds to voltages at the inputs. Or your proprietary driving techniques... '

The extra attenuators recommended to trim the advance pairs of signals (since the Scully uses two pairs (AR + PL; AR + AL - yes, advance right is needed twice, separately, at the inputs... which are all male, pin 3: High, btw), instead of three singles) are for the odd occasion, rather than the standard, in which case one would simply calibrate to the desired customary Base Pitch. It is rather for the rare spoken word disc, or super loud 12" single, that one needs to have the extra trimmers somewhere for those Preview adjustments (down,below, or up, above, the normally calibrated correlation to the Preview attenuator setting).


- Andrew

[gold]

Hi Andrew,

I think you will quickly change your theories once you start cutting. The max pitch on my lathe is 450LPI. That's a base depth of 2 mil with a half mil of land. At 600LPI with a half mil of land you would be cutting a 1.5 mil groove. And you will be getting complaints from everyone.

[Nickou]

Hi Andrew,

I think you will quickly change your theories once you start cutting. The max pitch on my lathe is 450LPI. That's a base depth of 2 mil with a half mil of land. At 600LPI with a half mil of land you would be cutting a 1.5 mil groove. And you will be getting complaints from everyone.

yes , 600 LPI is a bit too much ..

[Nickou]

check this out: http://www.diyrecordingequipment.com/1631/the-mcm-dac-mod-a-world-class-converter-for-under-150/

very interesting , did you do it ? how it is sounding ?
thanks for the input

[andybee]

http://www.diyrecordingequipment.com/

is fantastic site!

THANKS FOR THAT!

I got very big eyes!!!

[Serif]

Hi Andrew,

I think you will quickly change your theories once you start cutting. The max pitch on my lathe is 450LPI. That's a base depth of 2 mil with a half mil of land. At 600LPI with a half mil of land you would be cutting a 1.5 mil groove. And you will be getting complaints from everyone.

Hi Paul, I actually started cutting last year, even before you sent me the elliptical.

No problems with Base 400 and manual expansions to 192. My favorite pitch... What I'm working on now is cutting with the -76 Scully automation, since all my cutting hitherto has been fixed pitch. While I have stuck to a Base Pitch of 400, it has always intrigued me that tighter packing is quite available at up to 600 LPI while at just over 1.6 mil depth with ~20% land, or at a little deeper without quite overcutting... I'm sorry your lathe is limited in LPI. (;

Again, since this may not be getting through to some in the thread, using the number 600 as a Base Pitch is not at all the same as using 600 LPI as Fixed Pitch. The variable depth and variable pitch will keep this from being actually a 600 LPI cut except for the pregnant pauses and gossamer pianissimos... Not a typical cut - which is precisely why one needs the EXTRA attenuators for the two pairs of lathe inputs. There would already be a stereo attenuator for Preview on the console, but the additional ones allow the Feed or Depth to be tweaked independently for custom solutions on unique program, as you described, but also, in the case of the Scully (whence my question about the VA66), it is quite needed to temper the response to the input since it would be based on an erstwhile calibration to a standard Base Pitch which in this case is not being used.


Perhaps it is a good time to mention the Sontec Compudisk. This appeared at the same AES Convention as the first demonstration of the VMS80. Both computers are able to STOP the leadscrew for a fraction of a revolution, where program allows. This is a proper Contraction, as alluded to in my previous post. It says to itself, "You know, the Base Pitch is all well and good, but I can go even slower right here..." If your computer doesn't work this way, such as the LS-76 one, you must pick a Base Pitch which is high enough to save as much space as the program will allow.

- Andrew

[gold]

I'm sorry your lathe is limited in LPI. (;

450LPI is how I have it set up, not the capability of the machine. I think it will do 1,000LPI although I've never checked.

Again, since this may not be getting through to some in the thread, using the number 600 as a Base Pitch is not at all the same as using 600 LPI as Fixed Pitch.

I understand this but most pitch and depth systems have trouble offsetting more than 6dB without it being audible. If you set a base pitch of 600LPI and need an instantaneous change to 150LPI you will almost certainly get an over cut as it's beyond the capability of the system.

[Serif]

I'm sorry your lathe is limited in LPI. (;

450LPI is how I have it set up, not the capability of the machine. I think it will do 1,000LPI although I've never checked.

Oh.

I understand this but most pitch and depth systems have trouble offsetting more than 6dB without it being audible. If you set a base pitch of 600LPI and need an instantaneous change to 150LPI you will almost certainly get an over cut as it's beyond the capability of the system.

Not Scullys. Unless you mean instantaneous, and that is not needed. But 600 LPI might well be needed for LP sides which are unusual in program by today's lo fi pop standards, but for classical some experimental jazz and/or whatever, there is no rule against this (just as there is no rule of using a low pass filter or being always 3 or x mil Base Depth. Ask Bob Ohlsson, as I have. There's safe and compatible with el cheapo setups, and then there's vinyl audio fidelity.

Quieter is faster.

(6 dB is the reserve of the calibration to 1.228 VRMS, nominal on your Neumann and my Scully, both, but the additional attenuators are to work with non-cal'd Base Pitches.) Even the oldy Scully lathes were capable of 800 LPI for pianissimos with manual over-ride to 100 LPI or so. Here's a neat article interviewing Tom Fine's mom, who worked in audio for the Mercury hi end series (Living Presence)...

"...Until quite recently, recording lathes cut a fixed number of lines (grooves) per inch of diameter on every disk: 96 lines was most frequent for 78s, and for LPs it varied between 200 and 280 lines. Once the number of given lines for a given recording had been selected, it had to be maintained consistently from beginning to end. A certain "feed screw" was mounted into the lathe assembly, which moved the recording head steadily forward at the pitch selected. ("Pitch" is the distance the screw would advance in one revolution.) For soft music and little bass on the tape, the grooves were more widely spaced than desirable, with the result that the cut was uneconomical.

With high volume and strong low frequencies, the fixed pitch was too narrow to accommodate the passage in full, the engineer had to reduce volume and bass in order to prevent the stylus from overcutting the grooves. This meant serious loss of quality and fidelity which could be compensated in part only by expensive playback equalization controls. For years the Scully toiled on the problem, and by 1950 they had solved it: pitch variation at any given moment from 70 to 400 lines, or from 105 to 600 lines, or even from 140 to 800 lines per inch. Instead of several interchangeable feed screws with fixed pitches, a highly complex and smooth-working mechanism was devised and introduced into the machine, and today the engineer may set the advancing speed of the cutting head differently from moment to moment.

He can cut out a violin solo played in softest pianissimo at 600 or even 800 lines per inch, three times narrower than one could a few years ago; ten seconds later, when the whole orchestra's tremendous outburst with blaring trombones and tubas would have destroyed any master disk made by the earlier method, the engineer turns a knob and widens the groove distance to 70 or 100 lines per inch - and a smooth cut will engrave all the vigor and grandeur which had to be throttled away until recently..."

(from http://www.soundfountain.com/amb/mercury.html)


The LS-76 is over-ridable...




Your comrade in cutting remarks, hehe
Andrew

[tragwag]

wow, that is a great quote!
thanks