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DigiBeta Best Practices?

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Doug Stallard
DigiBeta Best Practices?
on Feb 4, 2008 at 12:31:55 am

Hey Everyone,

I apologize if this isn't the correct forum, I wasn't sure where to post a general DigiBeta question. Currently our facility ingests material from DigiBeta via SDI to various NLEs (mix of Matrox, FCP stations). Currently, our pre-ingest procedure is as follows:

Route test bars from NTSC Signal Generator (calibrated to be a known good signal) to our scopes. We then calibrate our scopes to this known good signal. We usually perform this step once a day just to verify the calibration on the scope. We then route the SDI signal from the DigiBeta deck to the scopes, cue up the tape to the bars and tone, and then use the controls built into the deck to calibrate the deck. We then perform our ingest.

Recently a colleague from another facility told me that there was no reason to calibrate a DigiBeta deck prior to capturing over SDI as this was a complete digital path, and the controls on the deck weren't actually doing anything to the SDI signal.

Now our facility is looking to purchase some additional DigiBeta decks, and it looks like we have two options: the DVW series and the compact J series. From the looks of things, it does not appear the J series has the same sort of controls we find on our older DVW-500 series (chroma, phase, video, etc.). I might be wrong, but I don't see them anywhere on the unit. So now I'm starting to wonder if there is some merit to what my colleague said?

Basically, my questions boils down to - Is calibration necessary when ingesting from DigiBeta over SDI, and if so, is it possible to calibrate the Sony J-series decks?


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Bob Zelin
Re: DigiBeta Best Practices?
on Feb 4, 2008 at 2:54:20 am

The J-30SDI is a fantastic VTR, and is commonly used by broadcast facilities. I don't know what you are looking at on your scopes, but when you do a dub from one SDI VTR to another, you are sending a digital signal from one VTR to the other - this is commonly called "making a clone" - because you are transfering the digital data.

The practice of looking at scopes, and aligning the TBC adjustments (in the DVW-500 series for example) is POSSIBLY aligning the analog out of the VTR. I dont' know what scopes you are using , and I don't know what signal from your VTR you are looking at. If you have an SDI Scope (like a Tek WFM-601, or a Videotek VTM-200, for example), and you are looking at the SDI output of your DVW-500, then THIS IS GOOD. But if you are looking at an analog color bar signal on an analog composite waveform monitor, and then looking at the analog output of a DVW-A500 on this analog scope, and aligning the color bar signal, and hoping that this will make your "digital clone" perfect, from one SDI VTR to another, then you are fooling yourself. However, if you are making dubs to a regular Beta VTR (like a BVW-75 or UVW-1800 for example), then you are doing the right thing.

You can drive yourself crazy with this stuff after a while. It is great that you have scopes, but I don't know what scopes you have. If you take the SDI output of a DVW-A500, and send this into the SDI input of an AJA or Blackmagic product, you will certainly affect the levels coming into these products with the TBC controls on the VTR - if you own an SDI scope, you should monitor the SDI output of the AJA or Blackmagic to see this. Theoretically, the signal was shot correctly, or transfered correctly, and when you input your SDI video (from your Sony J-30SDI) into your AJA or Blackmagic, the signal is correct, and if you want to make level adjustments, you can do this in with the color correction tool. This is a common practice today. Old school guys (like me), like to monitor the output of the NLE (just like you would monitor the output of your R-VTR or preview switcher in a linear edit system), but this is not a common practice today. Why ? Because most people don't own scopes - certainly not SDI or HD-SDI scopes.

Bob Zelin




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Doug Stallard
Re: DigiBeta Best Practices?
on Feb 4, 2008 at 3:46:52 am

Hey Bob,

Wow, thanks for getting back to me so quickly! Basically, here is our setup currently. We have 3 DVW-A500 DigiBeta Decks. All are connected via SDI to a SDI router. From there we can send the signals to our Tektronix SDI scopes, to our Sony SDI Broadcast monitor, or to one of several NLE systems via SDI. So, currently, are basic workflow for ingestions is as follows:

1. Route Tektronix Test Signal Generator via SDI to Tektronix Scopes
2. Use known good signal from the TSG to calibrate Scopes (if necessary)
3. Route signal from DigiBeta via SDI to Scopes
4. Cue up bars and tone on DigiBeta, use TBC controlls on deck to calibrate deck to NTSC levels and set audio to -20.
5. Route DigiBeta to NLE & Broadcast Monitor via SDI
6. Perform ingest while watching on Broadcast Monitor for problems with tape

So, what you're saying is that as long as the entire signal path is SDI, that calibration prior to ingestion is still considered a best practice at this point? If so, then I'm curious as I've just read the manual for the J-30SDI, and it specifically states that the controls on that unit for the Video Setup, Video Gain, Chroma Gain, Chroma Phase, and Setup Level "can be used only for video processing of the analog video signal. They cannot be used for video processing of the digital video signal (SDI/DV output). Does that mean that there is no way to control the signal as it goes out SDI? If so, what happens? Is there some sort of auto-calibration on the unit, or does it always run in some sort of "pre-set" mode? Or perhaps is calibration over SDI not really necessary? Can I trust these units to give the same quality signal as our older DVW-A500 decks? If not, should I only be looking at the new DVW series? And I think you're right, this is all starting to drive me a little crazy! I just want the most accurate results at the lowest cost.


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Bob Zelin
Re: DigiBeta Best Practices?
on Feb 5, 2008 at 1:56:11 pm

you know what - I DONT KNOW. I have clients that use Sony J-30SDI VTR's all day long (including Fox Sports), that have no TBC controls on them (there is no 15 pin remote on the back of a J-30SDI for TBC remote anyway), and they injest from this VTR with no level adjustment. "This is crazy" you say - you are correct, and I never even thought about it. There is this "digital is just perfect" mindset, which is of course, incorrect, and as you know the more expensive VTR's like the DVW-500, DVW-M2000, etc. have the adjustments, but as you observe the J-30SDI does not.

When you take a color bar tape (that was recorded on your DVW-500) and play it back in the J-30SDI, and observe the signal on your Tek 601 scope, are the levels incorrect ????

There is no "autocalibration" - when an SDI signal is sent in or out of a VTR, it is transfering digital data - which means that it is not changing the data - it's the same going in and going out (not increasing or decreasing levels) - just like this email. When I send this to you, it's a digital document. The font sizes don't INCREASE OR DECREASE, even though we are on different computers.

If this is an unacceptable answer for you, the CHEAPEST SDI Proc amp on the market (to my knowlege) is the Hotronics SDI Proc.

http://www.hotronics.com/
and look for the SDI Proc Amp. They have a rack mount version of this as well- it's about $1000 I believe.

Bob Zelin




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Bob Zelin
Re: DigiBeta Best Practices?
on Feb 5, 2008 at 1:59:42 pm

you know what - I DONT KNOW. I have clients that use Sony J-30SDI VTR's all day long (including Fox Sports), that have no TBC controls on them (there is no 15 pin remote on the back of a J-30SDI for TBC remote anyway), and they injest from this VTR with no level adjustment. "This is crazy" you say - you are correct, and I never even thought about it. There is this "digital is just perfect" mindset, which is of course, incorrect, and as you know the more expensive VTR's like the DVW-500, DVW-M2000, etc. have the adjustments, but as you observe the J-30SDI does not.

When you take a color bar tape (that was recorded on your DVW-500) and play it back in the J-30SDI, and observe the signal on your Tek 601 scope, are the levels incorrect ????

There is no "autocalibration" - when an SDI signal is sent in or out of a VTR, it is transfering digital data - which means that it is not changing the data - it's the same going in and going out (not increasing or decreasing levels) - just like this email. When I send this to you, it's a digital document. The font sizes don't INCREASE OR DECREASE, even though we are on different computers.

If this is an unacceptable answer for you, the CHEAPEST SDI Proc amp on the market (to my knowlege) is the Hotronics SDI Proc.

http://www.hotronics.com/
and look for the SDI Proc Amp. They have a rack mount version of this as well- it's about $1000 I believe.

Bob Zelin




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Doug Stallard
Re: DigiBeta Best Practices?
on Feb 8, 2008 at 4:47:42 am

Hey Bob,

Just wanted to drop a quick note to let you know how helpful you've been. For our situation which is digitizing content for archival purposes, it is extremely important that we're sure everything is valid on the initial capture. I've decided to go with the J-30 decks and the SDI Proc Amps that you suggested. I feel this will give us the same level of quality/control as the DVW models, but at about 1/3rd of the cost. Again, thanks for all your help!



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Nick Hrycyk
Re: DigiBeta Best Practices?
on Feb 6, 2008 at 11:49:17 am

One argument for leaving machines in unity, revisions! If you do your CC in the NLE, when it comes time to re-digitize for that inevitable revision 6 months later you stand a fighting chance of "matching" video to the original master.

Nick Hrycyk
Digital Image Studios


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Alan Okey
Re: DigiBeta Best Practices?
on Feb 9, 2008 at 7:02:34 am

[Bob Zelin] "when you do a dub from one SDI VTR to another, you are sending a digital signal from one VTR to the other - this is commonly called "making a clone" - because you are transfering the digital data."

Bob, I used to think this was the case, but I was shocked to learn that it's not. Check out this link:

http://www.kenstone.net/fcp_homepage/beyond_dv_nattress.html

Graeme Nattress certainly knows what he's talking about. Here's the relevant excerpt:

"Clone Dubbing

Some video recorders, such as Digital Betacam do not give the outside world access to the uncompressed data on the tape, so cannot be edited natively. This also means that you cannot do a perfect clone dub of a Digital Betacam tape.

The compressed output, which we use to edit a video format natively, can also allow a perfect clone of a digital tape to be made. You can easily make a perfect (within the bounds of dropout and data related errors which might, theoretically, over many repeated such dubs reduce the picture quality) dub by connecting a firewire cable from one DV deck to another, pressing play on the first and record on the second. Some DVCAM decks will also copy the timecode from the original over to the new copy too.

When tape-to-tape dubbing via an uncompressed SDI output you cannot make a clone copy. This is because the video must be uncompressed on the play-out machine, and then re-compressed on the recorder, which will theoretically reduce the picture quality (perhaps only slightly in the case of formats like Digital Betacam) and not be a perfect clone. In practice, dubbing from Digital Betacam to Digital Betacam over SDI is visually lossless over hundreds of generations, and indeed, the error correction used in Digital Betacam is so good that tapes with errors on them can often be improved through a Digital Betacam to Digital Betacam over SDI dub."


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