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Old February 13th, 2005, 05:41 PM   #1
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DV to Analog hell - beware

When was the last time you set, or were able to set, video levels on a calibrated waveform monitor while digitizing or dumping back to DV?

I suspect a lot of us have been lulled into complacency by the stability of the digital signal and the ease of digitizing and editing on Avid or FCP. After all, it looks great when digitized and it looks great when you do a digital cut back to MiniDV, DVCam, or DVPRO. It looks great on DVD. It even looks great when dumped out to Beta SP ...until you attempt to duplicate on to VHS for mass distribution. Playing back the analog, levels are all over the place. The blacks are through the bottom and the whites are off the scale.

This is what happened to us just this past week. We had done a job that was to be released on DVD. Unbeknownst to us, it was also going to be mass released on VHS. We finished the job last spring and had almost forgotten about it, until the calls began to come in from the client. Their duplicator was complaining the video levels were too high. The client complained some segments looked “blurry,” and sounded “fuzzy.” We had supplied the client with a Digi Beta copy of the master and a gold DVD master. The VHS was made from the Digi Beta. We asked for the Digi Beta back; when we put it through a scope – which hardly anyone bothers to use any more – the levels were indeed shameful - very embarrassing. Only way to fix it was to re-lay all the segments in the Avid using the built-in software based waveform “monitor” and vector scope. A great deal of manipulation had to be done to bring the video within specs.

We also discovered a problem with the audio. We had set the tone at -20 (Avid defaults to -14) but the duplicator set the playback tone at 0 which comes out as something close to +10 or +20 VU – in the red on the analog side. We still haven’t found the standard tone setting for digital since there’s a great deal of controversy on what the “standard” should be. We went with our sound mixer who uses -20.

I post this hoping to hear if any of you have encountered this problem when going to analog – especially VHS, and how you have gotten around setting video levels when digitizing on to an Avid (I assume the same holds true of FCP?)

Thank you for listening.
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Old February 13th, 2005, 06:11 PM   #2
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We haven't had hardly any problems with making dubs directly from DV tapes. We set audio levels at -20 db which is callibrated to 0db on analog sources, so if your levels stay with peaks at -20, then you should be ok. I have found that on our DV200 Panasonic cameras, the nominal range is really at -12db, which seems to be the standard for most consumer DV gear. In our DVCpro playback decks we just turn on DV attenuation, so when it detects a DV tape, it pads it to -20 db. So I'm not sure where you have your problems.
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Old February 13th, 2005, 06:49 PM   #3
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From a presentation I attended at Theatre Digital / FCPUGTO:

Digibeta tone should be at -20dbFS* (think of this as computer dB... the dB you see in Avid, Final Cut meters, .wav files, etc.).
*They did not use the term dbFS, but that's the term I use to refer to "computer dB".

Peaks should never exceed -8dbFS.

I'm not sure where average program volume is supposed to be... and there are several valid ways to measure average volume too.

From Jay Rose's book Great Sound for Digital Video (see dplay.com; excellent book, as is Audio Postproduction):

Dub Levels
pro digital formats:
-20dbFS nominal level, -10dbFS maximum for broadcast
-2dbFS maximum if it's theatrical.
Record -20dbFS tone at 1khz along with color bars at front of tape

miniDV: use -12dbFS for nominal level and tone. Maximum should not exceed -2dbFS.

Dubbing to analog: tone and nominal level should be 0VU. Peaks should not exceed +4VU on VHS, though betaSP can handle short transients as high as +6VU.

---
Extrapolating from this...

Digibeta master to VHS dubs:
tone at -20dbFS
I think this is right: -16dB maximum for peaks.
-20dbFS nominal level

Quote:
We had set the tone at -20 (Avid defaults to -14) but the duplicator set the playback tone at 0 which comes out as something close to +10 or +20 VU – in the red on the analog side.
I'd call them up as ask them at what level the following should be:
tone
nominal level
maximum level for peaks

If they can't tell you, I would either get a test dub done or look elsewhere.
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Old February 13th, 2005, 09:19 PM   #4
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Thank you for the comments. At least it shows that -20 is the unofficial "standard". I threw in the audio level problems as an afterthought. We do set tone at -20 - the duplicator for our client (we don't even know who that might be) set the digital playback tone at 0 - way too high, resulting in distorted analog audio as expected.

But that problem we can handle and the fix is simple - just put a big red label on the outside of the reels instructing where tone must be set.

It's the video levels that are driving us nuts. THAT's what I'd like to hear some comments about. How are you dealing with video levels in the digital - specially in the mid level digital domain?

oz
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Old February 13th, 2005, 11:32 PM   #5
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Quote:
Thank you for the comments. At least it shows that -20 is the unofficial "standard". I threw in the audio level problems as an afterthought. We do set tone at -20 - the duplicator for our client (we don't even know who that might be) set the digital playback tone at 0 - way too high, resulting in distorted analog audio as expected.
Ozzie, you should specify what the units are on those numbers.
In the digital domain, there's basically only one unit (dBFS).
In the analog domain, there's a whole bunch of units, but you're probably dealing with VUs (or decibels VU).
That's just a nitpicky communication thing... because "dB" can refer to dBFS, dbV, dbu, dB (SPL), and possibly a few others.

Anyways, the duplication probably set their tone at 0VU, or they didn't set it at all and used whatever previous setting they had. If it's the second case, -20dbFS should translate to 0VU anyways because the last setting was probably like that (anything else would be bizarre).

If the peaks in your program hit 0dbFS, then those peaks would translate to 20VU. For VHS, that would be way overmodulated. Don't peak that high. In Final Cut, if you hit play the meters will go and there will be a line that only gets pushed upwards (it never falls down). That indicates where your highest peak is. Use the numbers from my last post to figure out where it should be.

You don't actually have to peak that high... but if you wish to squeeze every ounce of loudness and/or dynamic range out of your master, then you can peak at the maximum.

Quote:
It's the video levels that are driving us nuts. THAT's what I'd like to hear some comments about. How are you dealing with video levels in the digital - specially in the mid level digital domain?
Feed bars and tone from your NLE (editing program) to your external scopes (hooked up to deck or monitor). Check that things are where they're supposed to be.

Bring up the vectorscopes in your NLE. Both sets of scopes should match... the middle pluge bar should be 7.5IRE in North America, and the white bar should be 100IRE.

Digression: If you don't have external scopes, you can't be sure what your video levels are. If you're working in the digital domain only then you can get away with the scopes in your NLE if they're set correctly.

Making your footage broadcast legal:
The brainless easy way: Apply a broadcast safe filter, and set the smoothness settings all the way. Use the extremely conservative setting. In Vegas this will actually work fairly well. Final Cut may work similarly... although I'm not sure if its broadcast safe filter has smoothness settings.

If you look at your video on a NTSC monitor, you may not like that as it compresses your highlights and shadows. Typically, it will be aesthetically pleasing. However, you are losing detail in the highlights and shadows. Clouds may look a little too blown out for your tastes. Colors will also shift in saturation (in addiction to brightness changes), which in some cases may be bad.

If you don't like the "brainless easy way" of doing things then you can get into more advanced color correction.

Once you're done color correcting, check your scopes so that blacks are 7.5IRE or above, and highlights 100IRE or less.

Color Correction in Final Cut
One good tutotial is http://www.kenstone.net/fcp_homepage/cc_legal_fcp4.html

If you use a curves filter like graeme nattress' one, you can achieve better results. That takes more explanation though.
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Old February 14th, 2005, 08:14 AM   #6
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I've never really noticed too many problems with video levels. Yes, it is important to look for broadcast legal, here in the US, but at the same time it usually goes the other way and the analog dubs are too dark. I wonder if maybe you have some faulty cables? You might want to check that out. Then it seems the best thing to do is take suggestions and experiment with your system. One other suggestion, would be to send your video thru a TBC before it hits the deck, unless of course you're using SDI.
Good luck.
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Old February 14th, 2005, 10:02 AM   #7
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The cables are all checked and fine. Besides, the material in question came from three different systems. It's just a matter of making sure the material is "legal" as it comes off the NLE. Since with DV masters there is not much one can do when digitizing, all the correcting has to be done afterwards and before it is sent back to a DigiBeta, DVCam, DVPro, and especially if it is being sent to an analog deck.

Bottom line - there is no free lunch. Whoever does the online has to go through the same process of checking the scopes (real scopes external to the NLE - not the software scopes built in). It is a slower and more expensive process, but it has got to be done. The apparent simplicity of DV can be deceptive and put everyone to sleep until it comes around to bite you where and when you least expect it.
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Old February 14th, 2005, 12:29 PM   #8
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This is why I still happily use my Pansonic MX-50.

I can completely control the upper clip and lower black where I want it. It does an excellent job.

You can also try using a stand alone DVD recorder, which has the same type of high end and low end auto black & white clip function, perhaps an EE through the system at it's highest quality setting although probably not a good idea because it will recompress your signal, unless the highest quality setting is considered lossless?
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Old February 14th, 2005, 12:47 PM   #9
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Yes, but clipping alone does not solve the problem. Unless the MX-50 has very sophisticated circuitry for clipping whites and blacks, clipping will usually result in ... well, obvious clipping which looks awful.
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Old February 14th, 2005, 12:57 PM   #10
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Obvious clipping?

It seems to do an excellent job.

The upper end is around 104-108 IRE clip, it's definitely not a hard clip. The lower end clip is done with the downstream keyer.

From what I understand most NLE systems offer different clipping options. I can clip on the fly if I want and it works great.
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Old February 14th, 2005, 01:31 PM   #11
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Alessandro,

I just took a look at the MX-50. It looks like an excellent switcher/processor. My question, and concern, is that it accepts analog inputs only. Is this correct? If so, it would severely limit us since the video would have to be transcoded from digital to analog and then back to digital. Do you know something that's not apparent to me?
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Old February 14th, 2005, 02:40 PM   #12
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I know some people are concerned about transcoding between analog and digital. I think having the video levels optimized is more important than worrying about the digital to analog and analog to digital conversions.
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Old February 14th, 2005, 05:47 PM   #13
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i can't understand why anyone would want to do vhs dupes! it's a dead end these days.

did you guys work with the audio levels using an external analog or digital audio meter? i can't edit without one, and i usually do the digital audio correction with the typical software that clearly shows when the peaks are crushed.

i once sent bad audio out to the vhs duplicator years ago, which is why i always monitor it with meters when making the master.

were you using an lcd ntsc monitor to edit with? not a flame, but i would have thought that blown-out overexposure would tend to be rather obvious, and nearly impossible to color-correct, if you were looking at it on any decent ntsc crt monitor.
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Old February 14th, 2005, 08:35 PM   #14
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Dan,

These are not VHS "dupes" as such. They are actual home vid "master" VHS for mass distribution in Asia and Latin America. I agree with you about VHS but that's not our call - it's the client's marketing strategy. Remember that this product was designed specifically for DVD distribution. DVD is still the prime distribution format but they must know there is enough call for VHS to mass duplicate. Had we known this was going to analog (and especially VHS) we would have been a lot more careful with our monitoring of levels.

The audio levels go back to the camera originals and the various sound people who took care of recording. Some of the bad stuff was shot in a studio with full audio - mics, 64 channel board, etc. And was mastered on DVCam, but by the time it got into the Avid Xpress Pro, there is not much one can do but play catch-up.

As far as the video levels go - they really are not obviously high or low. In fact, the DVD masters were not rejected and passed QA with no problem. We edit with an NTSC hires CRT monitor.

My original intent was to raise a red flag for everyone who has grown lazy with the instant gratification aspect of digital recording and editing. When was the last time you saw a CCU in the field? How many people are really editing with a close eye on a waveform monitor and scrutinizing audio levels? We got burned on this job primarily because we had become complacent with the speed and ease of shooting and editing with DV Cams and NLEs. I’ve been in the business for over 30 years, even with my background I was lulled to sleep by digital everything.

Do I feel foolish? You bet.
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Old February 14th, 2005, 10:37 PM   #15
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I get hired from time to time to do VHS remastering to BetaCam SP.

No, not precopyrighted material, but situations arise where the only master is on VHS. I would never make the final master onto another VHS. I would make it onto BetaCam SP after I've done a whale of a job color video and audio correcting all levels.

Yes, I use a waveform and vectorscope (and other goodies), all analog, and instant!

I'm confident the work I do staying analog is better than what anyone can do by using a standard consumer VHS for playback and trying to "adjust" in the NLE domain.
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