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Author Topic: V3 > 722 calibration  (Read 3964 times)

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Offline JasonSobel

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V3 > 722 calibration
« on: February 21, 2007, 09:52:27 PM »
ok, so what I want to do is run V3 (S/PDIF) > HD-P2 and at the same time go V3 (analog) > 722 line-in.
I want the levels to be spot on, so I don't have to change them in post and so that the comp will be perfect.

The 722, when going line-in, has a gain range of -6 dB to 18 dB
The 722 manual says that the line-in will clip at +26dBu (with the gain fully down)

When the V3 A/D meters are at 0 dBFS, the balanced analog output is at +25dBu

so, all I need to do is set the 722 line-in to -5dB, correct?  that way, the 722 will clip with a +25dBu signal, which is exactly what the V3 will be putting out over the analog output when the V3 A/D clips.  if I do this, in theory, the V3 levels will be identical to the 722 levels, correct?

I've thought this through and I'm pretty sure about this, but it's always a good idea to check on these sorts of things  :)

Offline gratefulphish

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Re: V3 > 722 calibration
« Reply #1 on: February 22, 2007, 09:36:42 PM »
The problem I and others have had, is that when you are running a V3 analog, you only want the meters to flash the first amber.  This results in a very low digital signal via the SPDIF to the other deck.  While your math may be correct, it presumes running the V3 hot, which you do not want to do when using it for analog out.
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Offline JasonSobel

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Re: V3 > 722 calibration
« Reply #2 on: February 22, 2007, 10:20:53 PM »
The problem I and others have had, is that when you are running a V3 analog, you only want the meters to flash the first amber.  This results in a very low digital signal via the SPDIF to the other deck.  While your math may be correct, it presumes running the V3 hot, which you do not want to do when using it for analog out.

I realize that when the V3 is run hot, it causes a problem for the analog outputs, because most recorders cannot handle that hot of a signal.  the "first amber", though, is really just a rule of thumb, and is very dependant on what you are running analog into.  As I read the specs, the 722 can handle the analog signal, even when the V3 is run hot.  I'm really just trying to confirm that I'm reading the specs correctly.

Offline JasonSobel

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Re: V3 > 722 calibration
« Reply #3 on: February 23, 2007, 07:14:04 AM »
ok, let's talk hard numbers here.

from the V3 manual, this is what the analog outputs are doing:

LED Color.............dBFS...................Balanced Analog Out (dBu)
Red0+25
Amber-3+22
Amber-6+19
Amber-9+16
Green-12+13
Green-15+10
Green-21+4
Green-27-2

ok, now, the 722 specs state that line-in, at minimum gain (i.e. -6dB), it will clip at +26dBu.  given that, with 0dB of gain on the 722, it should clip at +20dBu

now, let's take a close look at what Moke says:

4022's -> V3 analog -> 722 line-in, at 0db gain

with the above rig, and settings, I can only light up the first ambers and still maintain a wee bit of headroom. This brings me up to -4  / -3 digital peak level. If I light up two ambers (2nd set of non-greens) i need to run attenuation of the 722.

ok, the if the peaks are at the first set of amber LEDs on the V3, that's a digital level of -9dBFS.  at that peak, the analog out is at +16dBu.  because the 722 will clip at +20dBu with 0dB of gain, the peak digital level on the 722 will be -4dB.  which is entirely consistent with what Moke is saying. ("digital peaks at -4 / -3"...  so if you're 722 peaks at -3, it means that you are really getting to -8dBFS on the V3, so the first amber LED is lit, but the second one is not yet lit up)

so, what I'm saying is that I could run the 722 at -5dB in line-in mode.  the 722 will then clip at +25dBu.  now, when the V3 levels hit the RED (i.e. 0 dBFS), the V3 balanced analog output is +25 dBu.  so, the digital levels on the V3 should be identical to the digital levels on the 722, because they're both clipping at the same point.

maybe it's not "ideal" to run the 722 line-in at -5dB (and if I ultimately decide to buy a SD unit to run from the V3, I'll probably run line-in at 0dB).  BUT, running at -5dB on the 722 line-in should provide a very accurate comparison between the V3 A/D and the 722 A/D, because the digital levels will be spot on.

can anyone confirm all this?  am I reading the specs correct?  based on the short analysis of Moke's experience, and based on my reading of the specs of the two units, I'm 98% sure that this would work just as I'm saying.  maybe I should just run a test this weekend, with a sine-wave test tone or something, just to check the levels on everything.
« Last Edit: February 23, 2007, 07:37:52 AM by JasonSobel »

Offline Todd R

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Re: V3 > 722 calibration
« Reply #4 on: February 23, 2007, 04:23:20 PM »
Jason --

From the numbers, it sounds like you've got it right.  I just got my new (used) 722 today  ;D -- so I'll start playing around with it this weekend.  I'd like to be able to do just what you are saying and get the V3(digi)>MT and V3(ana)>722 dialed in so I can do some A/D comparisons without needing to normalize levels in post.

Let us know what you find out!!
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Offline JasonSobel

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Re: V3 > 722 calibration
« Reply #5 on: February 23, 2007, 07:12:02 PM »
Jason --

From the numbers, it sounds like you've got it right.  I just got my new (used) 722 today  ;D -- so I'll start playing around with it this weekend.  I'd like to be able to do just what you are saying and get the V3(digi)>MT and V3(ana)>722 dialed in so I can do some A/D comparisons without needing to normalize levels in post.

Let us know what you find out!!

nice :)

I'll try to run a couple of tests this weekend for confirmation, but I probably won't get a chance to run the A/D comp until another couple of weeks.  if you find out anything with your testing around, please let me know.  and I'll definitely post the results of any testing that I do here.
« Last Edit: February 24, 2007, 08:10:48 AM by JasonSobel »

Offline JasonSobel

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Re: V3 > 722 calibration
« Reply #6 on: March 14, 2007, 07:34:20 PM »
I finally got around to a quick test of this, because tomorrow night is my big comp: V3 A/D vs 722 A/D.
so, I want the levels to be right on.  I just did a minute long test in front of my home stereo.

V3 > S/PDIF > HD-P2
and
V3 > analog > line-in 722 (-5 dB)

both recorders at 24/96.

after transferring the files to my computer, I went into WaveLab and trimmed the start and end of the two files so that they start and end at the same point.  I then did an analysis to see how the levels turned out.

here are the results:
HD-P2 levels:


and

722 levels:


so, if we look at the average RMS values, the left channel is within 0.04 dB between the two recordings, and the right channel is within 0.06 dB between the two recordings.

I am thinking that this is very good level matching between the two recorders, and that my full-on comparison tomorrow night will be a wonderful comp between V3 A/D section and the 722 A/D section.

but I was still curious about the tiny discrepencies.  I think this is the reason:  because I did not use wordclock to sync the two files, even though I trimmed the two files to start and end at the same place, the files from the 722 was actually slighty longer, as evidenced by this shntool output:



from that, we can see that the file from the 722 is 0.003 seconds longer than the file from the HD-P2, which is roughly 288 samples at 96 kHz.  so, it is entirely possible that the very slight level variations are from the different number of samples being analyzed between the two files.  unfortunately, I do not have a BNC > BNC connector, otherwise I would run word clock out from the V3 to the wordclock input on the 722 (my V3 is not an opti-mod). 

anyone have any other suggestions as to why the levels are slightly off.  (of course, with levels that close, I don't think people will really be able to detect that small difference, and that won't affect what people think of the comp.)

BUT, I think my comparision will still be valid, even with the different digital clocks.  it looks like the levels will be spot on, and I have no intention of ever mixing the two sources, so the slight time drift will be a non-issue for me.

so, this brief test of mine indicates that the published output levels on the V3 and the published input levels on the 722 are spot on.

and as a side bonus, this was the first time I ever used the analog outs on the V3.  by running from both the analog and digital outputs, I was able to verify that Grace did indeed fix the polarity of the digital output relative to the analog outs.  not that I ever doubted it after getting the unit back from them, but it's nice to see right in front of me that the two files were of the same polarity :)
« Last Edit: March 14, 2007, 07:39:42 PM by JasonSobel »

Offline Todd R

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Re: V3 > 722 calibration
« Reply #7 on: March 15, 2007, 12:12:01 AM »
Excellent Jason!!  Thanks for the testing!

I did run the 722 with the levels set at -5 as you suggested for Bustle in your Hedgerow.  I didn't do the great follow up testing you did, but running digi out of the V3 into my MT and analog out of the V3 into the 722.  The -5db calibration worked great.

BTW, I did just finish a 1 hour test of recording mics>V3(digi-optical)>h120 and 2nd mic pair>722, with V3(digi-coax)>722 for clock sync.  The V3 digi signal went into the AES3 BNC input (not clock input) of the 722, with mics into the XLRs and the 722 manually set to accept analog inputs, not auto select.  The 722 locked perfectly to the V3's clock.  I checked the files over the course of the hour-long recording -- no clock drift.
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Re: V3 > 722 calibration
« Reply #8 on: March 15, 2007, 12:38:51 AM »
Ok, I just pulled up my Bustle files and used CoolEdit to analyze them.

Average RMS power, V3:
L:  -19.29    R:  -19.51

Average RMS power, 722:
L:  -19.07    R:  -19.27


So 0.22db variance on the L channel, and 0.24db on the R channel.

Not quite as accurate as you found, but far close enough for my taping needs.  I didn't put a huge amount of effort into trimming the files exactly though, so that might explain the difference.  I was fairly close with the trim points, but the files still varied by about 200ms total in length in the end.
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Offline branas

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Re: V3 > 722 calibration
« Reply #9 on: May 11, 2007, 11:44:07 PM »
Wow, thank you guys, this is exactly what I needed to know.
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Offline nedstruzz

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Re: V3 > 722 calibration
« Reply #10 on: June 28, 2007, 03:24:08 PM »
Very good read, but keep in mind that by attenuating the 722 source by -5db you are changing the quality of the signal going to the 722 AD stage. 

After reading the responses and notes from the AD comp I think it is safe to say that the V2/3 pre amp is what we all knew it was and the 722 AD is slightly superior then the V3's. 

Wonder what specifics internally make the 722 AD sound slightly better then the Lunatec?
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Offline it-goes-to-eleven

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Re: V3 > 722 calibration
« Reply #11 on: June 28, 2007, 04:27:02 PM »
Wonder what specifics internally make the 722 AD sound slightly better then the Lunatec?

Perhaps a more shocking question is why has v3 > r09 beat out the v3's internal A/D in the 2 or 3 comps we've run here?  I'd hardly believe it if it weren't for multiple comps and that it was my gear.

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Offline nedstruzz

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Re: V3 > 722 calibration
« Reply #12 on: June 28, 2007, 04:53:28 PM »
There is defintaly something weird about that Grace AD. 
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