Green Flicker #200
Comments
|
Looks like it could be a tbc error,but that's usually straight lines,yours looks like quite a distinctive pattern. We have the same deck and I haven't seen it show up.could you share a video in the original encoding of the error with a few frames either side?I'd love to see it in qctools.. |
|
This is probably not the best way to do it, but below is a 30 second video of it. The flicker isn't something that shows up for 15 seconds and then disappears, its always present. https://www.youtube.com/watch?v=ptogAuUHlq4&feature=youtu.be |
|
Thanks for sharing! I won't really be able to help any further, but it
would be great if you could share an uncompressed/lossless version of that
clip on the internet archive. I think even two or three seconds would
suffice. I'd still like to investigate it further, and more knowledgeable
people than me could have better insight with a higher res clip. I'd like
to see the original interlaced version and some extra detail in the chroma
channels rather than the 4:2:0 youtube version.
…On Wed, Jun 6, 2018 at 8:20 PM, ChrisNicols ***@***.***> wrote:
This is probably not the best way to do it, but here is a 30 second video
of it. The flicker isn't something that shows up for 15 seconds and then
disappears, its always present.
https://www.youtube.com/watch?v=ptogAuUHlq4&feature=youtu.be
—
You are receiving this because you commented.
Reply to this email directly, view it on GitHub
<#200 (comment)>, or mute
the thread
<https://github.com/notifications/unsubscribe-auth/ABEyvhByhCDhN0ggUe_-WqT1jwZIdD-Aks5t6Ct9gaJpZM4UdNKw>
.
|
|
Aliens 👽 |
|
Ah,only seeing the qctools report in your edited comment now. |
|
I will upload the video tomorrow. Its taking a long while to upload to the Internet Archive |
|
Hi, everybody.
Chris, does it only happen with a series of tapes from a certain collection, or does it happen randomly with tapes that are from different collections, recorded in different machines?
Because of the location and color of the artifact, I would guess that this could be due to a difference in mechanical alignment between the machine that recorded the tape and your UVW-1800. It looks like the tape might not be making good/even contact with the video drum after it passes the entrance guide. I usually associate that type of muted green flickering artifact in Betacam playback with an error that is not fully correctable by the integrated TBC, as opposed to a recorded-in-souce problem or a physical tape defect (more saturated green can show up even with small head clogs and dropout in Betacam, though).
If this isn’t happening in other Betacam machines with the same tapes, you might want to have an alignment check on your 1800.
- Michael A.
On Jun 6, 2018, at 12:35 PM, kieranjol <[email protected]<mailto:[email protected]>> wrote:
Thanks for sharing! I won't really be able to help any further, but it
would be great if you could share an uncompressed/lossless version of that
clip on the internet archive. I think even two or three seconds would
suffice. I'd still like to investigate it further, and more knowledgeable
people than me could have better insight with a higher res clip. I'd like
to see the original interlaced version and some extra detail in the chroma
channels rather than the 4:2:0 youtube version.
On Wed, Jun 6, 2018 at 8:20 PM, ChrisNicols ***@***.******@***.***>> wrote:
This is probably not the best way to do it, but here is a 30 second video
of it. The flicker isn't something that shows up for 15 seconds and then
disappears, its always present.
https://www.youtube.com/watch?v=ptogAuUHlq4&feature=youtu.be
—
You are receiving this because you commented.
Reply to this email directly, view it on GitHub
<#200 (comment)>, or mute
the thread
<https://github.com/notifications/unsubscribe-auth/ABEyvhByhCDhN0ggUe_-WqT1jwZIdD-Aks5t6Ct9gaJpZM4UdNKw>
.
—
You are receiving this because you are subscribed to this thread.
Reply to this email directly, view it on GitHub<#200 (comment)>, or mute the thread<https://github.com/notifications/unsubscribe-auth/AIZAni6ZFFf-c3y3SOdCzYCJ2xqv1Lakks5t6C8TgaJpZM4UdNKw>.
|
|
Thanks, Michael. I will get to a more detailed response tomorrow, but I'm just about to leave for the day. In the mean time, here is a link to the video file itself: |
|
@ChrisNicols can you add this error to the AVAA? 😺 |
|
Michael, Thank you for your detailed response. I have digitized around 50 tapes on this particular UVW-1800 and only started seeing the problem with this most recent set of tapes. When I go back and play old tapes I know worked, the green flicker issue does not occur. I would think it must be the tapes then, but for two things: 1. When played through another UVW-1800, the green flicker issue does not manifest, and 2. Some of the tapes from the same collection or set do not exhibit the green flicker issue. I am reluctant to trust the results of the second UVW-1800 because it is also experiencing some unrelated issues on every tape, exhibiting drop out on tapes that I know do not suffer from dropout. I tried running the first UVW-1800 through my DPS-290 after turning off the internal TBC, but there doesn't seem to be any improvement. I agree that generally, it seems like the tapes are not making full contact with the video head. At the very beginning of some of these tapes, the green flicker dips down even further in the picture and the color information is lost on the upper third of the screen for a second or two. The green flicker does not seem to be consistent in shape. I'm afraid I don't know which tapes were recorded in which machines. The only provenance I have is from the holding repository. The tapes have been stored in poor conditions for the last 20 years- 60-70F and 60-70% RH, with fluctuations in the summer months of 20-70% RH every day/night cycle. I have seen a lot of skew errors on other tapes all going off to the left, so I'm worried that the tapes have deformed over time and thats just made some special conditions with these tapes even worse. If its just this selection of tapes, then I guess what I need to do is fix the dropout issue with my second Betacam machine and just capture these tapes in that one, since its alignment doesn't seem to have a problem. I've cleaned the head with static/lint free wipes and cotton swabs as much as I can, but there's still no difference or reduction in dropout. Sometimes, the little dropout flickers actually look almost like that green flicker- like its not quite flush with the video head. This flicker is at a different part of the screen, though, it doesn't look like its part of some larger, descending problem. |
|
@ablwr I will add the error this afternoon. EDIT: Actually, on second thought, I will wait until I've gathered more info. I dont want to create redundant articles if its a pre-existing issue. |
|
😺 😺 😺 |
|
Should I start a new entry about Head Misalignment? |
|
HELL YEA |
|
Actually, just as a follow up, does anyone know how to access the tracking control function of a UVW-1800 Sony Betacam machine? Someone suggested it might help with the problem. |
|
I'll reach out to some techs and see if I can dig up a manual |
|
I think I found a manual, but I didn't see any indication of tracking controls. I'm probably just missing something obvious, and any help is appreciated. |
|
Hi Chris,
I’ve used that deck a lot in the past, but I don’ remember it ever having a tracking control (we don’t have an 1800 right now). The PVW and BVW series machines have one, but due to the comparatively good accuracy of the control track pulses with the Betacam system, it’s not usually necessary to adjust tracking in most cases. If I remember correctly, the UVW series was intended to be a low cost option for Betacam playback and its features were limited, so I don’t know if there is a good way to adjust tracking outside of actually doing an alignment on the machine.
Without knowing exactly what this artifact is, it might make sense to put it in the “unknown artifacts” category. If I had to come up with something right now, I’d probably put it in the Time Base Error category of artifacts, with a description like “time base error related to difference in mechanical alignment between record and playback machines (Betacam)”. I noticed in QCTools, using the “extract planes equalized” filter, the artifact appears similar to “flagging” (see attached image). The green color may be a result of the way that the VTR electronics are trying to correct the problem, but it still looks similar to flagging, which can fit into the category of time base error.
On Jun 7, 2018, at 9:06 AM, ChrisNicols <[email protected]<mailto:[email protected]>> wrote:
Michael,
Thank you for your detailed response. I have digitized around 50 tapes on this particular UVW-1800 and only started seeing the problem with this most recent set of tapes. When I go back and play old tapes I know worked, the green flicker issue does not occur. I would think it must be the tapes then, but for two things: 1. When played through another UVW-1800, the green flicker issue does not manifest, and 2. Some of the tapes from the same collection or set do not exhibit the green flicker issue.
I think this points back to the specific UVW-1800 that is exhibiting the artifact and its different mechanical alignment. This set of problem tapes may have been recorded on a machine that had a different tape path alignment, which may or may not cause the artifact to appear on another playback machine (if its alignment is closer to the original record machine’s set up, for example, the artifact wouldn’t show up). Without knowing if this specific set of tapes that are causing the artifact to appear were recorded on a machine that was aligned properly, you get into a “chicken or egg” situation. But if these are the only tapes from the collection where it appears, I would guess that the record machine used to make them is where the problem originated. This is one reason that the right time base corrector can be useful because they’re meant to fix these types of problems. Sometimes they can and sometimes they can't, but it really depends both on the severity of the problem and the pairing of specific machine and model of time base corrector. These tapes may also have stiction issues that are exacerbating the time base error. I’m not sure if upper drum wear would cause this type of artifact under the right circumstances, but I suppose that’s yet another possibility.
I am reluctant to trust the results of the second UVW-1800 because it is also experiencing some unrelated issues on every tape, exhibiting drop out on tapes that I know do not suffer from dropout. I tried running the first UVW-1800 through my DPS-290 after turning off the internal TBC, but there doesn't seem to be any improvement.
Do you only have the DPS-290? I assume you don’t have access to a cleaning machine. It could help improve this issue if stiction is part of the problem. If you can find the service manual, you can check the drum rotation and tape running hours to see if they are astronomical (would indicate they at least need service and potentially a new upper drum… especially if you’re playing really dirty tapes or tapes with stiction issues).
I agree that generally, it seems like the tapes are not making full contact with the video head. At the very beginning of some of these tapes, the green flicker dips down even further in the picture and the color information is lost on the upper third of the screen for a second or two. The green flicker does not seem to be consistent in shape.
When all of the tape is on the supply reel, there will be more drag on the transport due to a difference in tape tension (especially if there is stiction), which may account for the change in severity at the beginning of some tapes. This is probably another clue that this is related to time base error caused by difference in mechanical (possibly guide) alignment. But as mentioned before, this would be exacerbated with stiction, for example.
I'm afraid I don't know which tapes were recorded in which machines. The only provenance I have is from the holding repository. The tapes have been stored in poor conditions for the last 20 years- 60-70F and 60-70% RH, with fluctuations in the summer months of 20-70% RH every day/night cycle. I have seen a lot of skew errors on other tapes all going off to the left, so I'm worried that the tapes have deformed over time and thats just made some special conditions with these tapes even worse.
If its just this selection of tapes, then I guess what I need to do is fix the dropout issue with my second Betacam machine and just capture these tapes in that one, since its alignment doesn't seem to have a problem. I've cleaned the head with static/lint free wipes and cotton swabs as much as I can, but there's still no difference or reduction in dropout. Sometimes, the little dropout flickers actually look almost like that green flicker- like its not quite flush with the video head. This flicker is at a different part of the screen, though, it doesn't look like its part of some larger, descending problem.
Rather than fixing the dropout issue with the second Betacam machine, you could also try to have some routine service performed on the UVW that is exhibiting the problem. Depending on the cause of the dropout problem, it might be more cost effective to have the first machine serviced (but that could depend on some other factors, as well).
P.S.
Are you using the cotton swabs on the heads? I would avoid that… If the cotton fibers get stuck on the tips, you’ll damage them. The lint-free cotton cloth pads are good (or chamois tips, but they’re too expensive).
- Michael A.
[cid:[email protected]]
|
|
Thanks Michael, That is a lot of very useful information for me to consider. I'm just finding out that our playback decks have not been serviced for a long time, so before I make any more concrete judgments about whats going on, that needs to happen. Other AV archivists I've talked with so far seem to think its some kind of misalignment issue as well, but I'm sure the lack of maintenance is only exacerbating it.
In addition to the DPS-290, I also have some AVT-8710s that I'm using for VHS tapes. I assumed they would not be as powerful as the DPS-290, but Im open to suggestions.
I'm finishing some trial runs on our new tape baking oven this week, so I will try baking a few of them next week and let you know how it goes.
Thank you for the advice, this was something I learned from a former supervisor, but yes, it is very easy for the cotton to tear off into the video head. I will cease that practice. I saw something really weird today with one of the tapes. It was a tape full of b-roll material, so lots of starts and stops. The first five minutes of the tape were fine, but then a new shot started and it had the green flicker issue for the second five minutes. There is another tape that has part two of one of the interviews on the b roll tape from the green flicker portion, and it looks perfectly fine. Is it possible that the issue is actually the result of edge damage or tape deformation? |
|
Since I met a few people watching this thread last night, I just wanted to update everyone on the article I need to write about this issue. My immediate supervisor is excited for me to provide examples and write about what we're doing at the NYC Municipal Archive, but we just need to get it OK'ed by the head of the archive, first. Hopefully this afternoon or next week. EDIT: I also just wanted to thank everyone who has been so generous with their time and their kind words of encouragement. I'm just finishing our first tape baking experiment this afternoon and there are a lot of other A/V artifacts and issues I would love to provide examples of in the future. |
|
Hi Chris,
I'm just finding out that our playback decks have not been serviced for a long time, so before I make any more concrete judgments about whats going on, that needs to happen. Other AV archivists I've talked with so far seem to think its some kind of misalignment issue as well, but I'm sure the lack of maintenance is only exacerbating it.
If you need recommendations for service providers (and you are willing to ship), I can give you some contact info for people that we use.
Do you only have the DPS-290? I assume you don’t have access to a cleaning machine.
In addition to the DPS-290, I also have some AVT-8710s that I'm using for VHS tapes. I assumed they would not be as powerful as the DPS-290, but Im open to suggestions.
The only cleaning machines I found were much too expensive for us to afford, something like $3,000. If you know of any cheaper alternatives, I (and I think a lot of other people) would be very interested.
You would need to use a TBC with a Y/R-Y/B-Y input, and I don’t think the AVT has anything but composite and S-Video. There are some 90’s era TBCs that I have found to be more effective with Betacam, but they are harder to find in serviceable/refurbishable condition.
Unfortunately, I don’t know of any options in terms of inexpensive cleaning machines. There has been development work on DIY machines, but not really with cassette formats, as far as I know. The mechanics involved with cassette cleaners are significantly more complicated because of loading/threading processes and the inherent risk involved with moving tape suffering from binder hydrolysis in/out of the cassette housing during cleaning. I wish I knew of a cheaper way to get access to a cleaning machine, but this is another well-known, big problem that we have yet to solve.
When all of the tape is on the supply reel, there will be more drag on the transport due to a difference in tape tension (especially if there is stiction)
I'm finishing some trial runs on our new tape baking oven this week, so I will try baking a few of them next week and let you know how it goes.
Are these Betacam (oxide) or Betacam SP (metal particle)? So far, I don’t think I’ve found stiction problems with SP tape formulations that couldn’t be resolved through cleaning. The tape characteristics and binder are different than other, older analog tape formats. We have baked Betacam oxide tape when necessary, which can be treated similarly to VHS/Betamax for heat treatment, although I believe the oxide is less dense with those stock types than Betacam coatings. The red lid Ampex oxide tape in particular often needs baking - can’t remember the stock offhand. We clean a lot of Betacam SP, and I’ve found that it can significantly improve performance. If these are SP tapes, you may want to contact a specialist (i.e., Peter Brothers) before you decide to bake them. I think he recently told me it can be effective in some cases, but there is a specific method to use for that process, and he may be able to help you with it. I would probably advise against baking SP tape unless you can confirm there is a moderate to severe stiction problem (i.e., squealing, jamming transport nightmares, etc) and you can get advice from someone who does it more regularly.
Are you using the cotton swabs on the heads? I would avoid that…
Thank you for the advice, this was something I learned from a former supervisor, but yes, it is very easy for the cotton to tear off into the video head. I will cease that practice.
I saw something really weird today with one of the tapes. It was a tape full of b-roll material, so lots of starts and stops. The first five minutes of the tape were fine, but then a new shot started and it had the green flicker issue for the second five minutes. There is another tape that has part two of one of the interviews on the b roll tape from the green flicker portion, and it looks perfectly fine. Is it possible that the issue is actually the result of edge damage or tape deformation?
There are enough variables now that I wouldn’t rule anything out. You can find the portion of tape that is exhibiting the artifact and inspect it to see if it is warped or otherwise damaged (it might work best if you can take it out of the shell). The fact that you’re getting different results in different machines, both of which probably need full routine maintenance (or at least need to be checked for alignment problems), make it harder to come up with a hypothesis. Inspecting for warped tape or some other physical problem is certainly a good idea, and a warped tape may affect tape-to-drum contact in a similar way to a misaligned guide. I suppose it is possible, but I would say unlikely, that a noticeably deformed tape would give significantly different results between two different machines. If a Betacam tape is damaged enough to be artifact laden in one machine, it will likely be the same in another. Although again, without knowing the condition of the upper drum and that the guide alignment, tension and other parts of the tape path are adjusted within tolerance for consistently reliable playback in one of the machines, it is hard to say that conclusively.
—
You are receiving this because you commented.
Reply to this email directly, view it on GitHub<#200 (comment)>, or mute the thread<https://github.com/notifications/unsubscribe-auth/AIZAngl2j-__zHpUczgA1cimGrUQU6NKks5t8ozAgaJpZM4UdNKw>.
- Michael A.
|
I would love recommendations in the NYC area. Currently I have been advised by several MIAP alumni that http://www.alartvideo.com/ is very good and speaking with the owner over the phone was very informative. That being said, we have not made a final decision.
Thats an interesting piece of information. I dont have the opportunity to get new equipment any time soon as we just got the tape lab set up and we have a film scanner coming in October to digitize a bunch of these NYPD Illegal Surveillance films, but something to keep in mind for future projects.
Its a mix, not just of Betacam but of several tape formats. Right now, we're just dealing with Betacam, Betacam SP, U-matic and VHS- but these issues are only showing up on Betacam tapes. I have a U-matic tape that is just a classic example of sticky shed that I'm looking to bake with a food dehydrator I modified and I want to heavily document that process. I will definitely hold off on baking any Betacam SP tapes, though. I've baked under supervision, but never on my own. Think you could send me the contact info for Peter Brothers?
I agree, I need to get these decks repaired before I can start saying anything conclusive. For now, I've uploaded an example image and short description to the AVAA entry on Time Base Errors. If I find out more, maybe after the decks get serviced, I will either update the article or make a new one. I also got the go ahead from Archives Director to start making blog posts about our project digitizing WNYC-TV tapes, so I hope to have a lot more examples of technical issues we're dealing with. I'll make less technical blog posts on http://www.archives.nyc/blog/ and try to write up something more technical for AMIA, both about this green flicker issue and the new lab set up at the NYC Municipal Archives. Let me know if there are any other portals I should post this to. I know we're planning on submitting one of our newly created videos to SAA in Washington DC this summer. |
|
Peter Brothers |
I've started noticing a weird green flickering artifact at the top of my Betacam tapes. At first I thought it was just a series of tapes with a unique tracking problem. I ran it through a different Betacam machine and didn't see the flickering green artifact anymore, so now I'm starting to worry my Sony Betacam UVW-1800 is dying. I'm a little doubtful of that, though, because this green flicker doesn't show up on all tapes in that machine and only appeared recently.
I've tried thoroughly cleaning the video head with both a cotton swab and static/lint free wipes with isopropyl alcohol, but there doesn't seem to be any difference. I am including some examples of the flicker.
The text was updated successfully, but these errors were encountered: