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Discussion Starter · #1 ·
I guess this question is more directed towards Dave since he probably has more experience with this machine than anyone (but all others are welcome with their observations). I just received my unit today and watched the demo tape. In a word, SUPERB. The color & clarity was absolutely breathtaking. As you guys know, the tape has 2 complete "play throughs" of the demo. The first complete demo (first 1/2 of the tape) played through without a video or audio glitch. However, the 2nd half of the repeated demo had 2 video & 1 audio glitch within a 15 second period (during the "automn in N.Y." segment). The interesting thing was that these glitches were REPEATABLE. I rewound the tape and replayed it and each glitch essentially duplicated itself. The audio glitch occurred at the same point each time as well as the 2 video glitches (not a blackout, but a partial "mosaic" effect common with digital video glitches). One video glitch manifested itself in slightly different ways on repeated playings, however it was always in the same spot but the other was virtually identical each time. SO, the question is, is this a tape issue or is this a machine issue (very little tolerance for error?). If I played this same spot on another JVC would it play fine or would most JVCs show the same glitch with this particular tape? Once again, aside from these glitches, the video quality is just superb.


Oops. Forgot to mention I checked my serial # and the unit has the latest software.


Thoughts anyone?
 

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I have not watched the demo tape all the way through but anytime I have been able to rewind the play with the dropout at exactly the same place, I have always said tape issue. I therefore would not worry about the machine.


I remember when dvd's first came out (and still have this issue some times) They were having issues making the discs some times, and some discs would not play in certain machines.


This is why I am very very interested in the folks getting the new D-Theator release tapes. Are they playing perfect or are there gliltches?

What happens on a rewind area where it had the glitch. Is it still the same place. Until we have some more data with more tape types, I am only will to be in the data collection mode rather than judgment. Even at worst case, I still would rather live with a few glitches on D-THeater HD tape than a "perfect" dvd.


dave
 

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Discussion Starter · #3 ·
Dave,

Interestingly I again watched the 2nd half of the demo at the "automn in N.Y." piece and it seems I'm actually getting more video glitches than before. The original ones are still in the same spots. It's only during this segment and doesn't show up in the same segment in the first half of the tape. I'm wondering why the dropouts are actually increasing in this area. It doesn't seem the error correction in this format is as effective as it is in mini-DV. But WOW that picture!! I'm really hoping the movies don't suffer from this issue.
 

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Ken,


I have the same sort of problem with the "Yes" D-theater tape: dropouts and pixelation always repeating in the same place on the tape. Demo, and Motley Crue play thru flawlessly. My 30kU has current firmware.


I found that I could use manual tracking to produce clean playback from those "bad" spots. All it took was one or two clicks to fix the playback, but then pixels would show up in new places. I guess the autotracking is not sensitive enough to keep the entire tape in focus, at least for some marginal tapes.


I suspect the JVC's are poorly aligned. I'll know more about this after I do a little tweaking.
 

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As I say, lets get some more data since I have not written off there is a problem.


This is one area where I can say from what I have heard, the Mits is a much better deck in terms of tracking. They also seem to be able to play S_VHS decks better.


Now see, I do admit what product has better features, and I dont have a Mits.


Todd and Don you are much better off here with your Mits.


Dave "The half full guy"
 

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Discussion Starter · #6 ·
gridleak,

This a bit disconcerting to hear. The problem then is not isolated to the demo tape. I suspect you're right about the poor alignment as the potential cause. In a way though, that may be better than writing this off to extremely fragile tape. Tape would have to be reformulated but alignment can be fixed with better QC right off the bat. Having had many many JVC SVHS units, I can attest to poor longevity with these units. The only thing that's surprising is that they generally work perfectly at the beginning, produce better pictures than other brands, but don't last. It's concerning that these D-VHS units show glitches right out of the box. Ofcourse some owners report never seeing dropouts with any tape. We really need to keep our eyes on how the movies play. I've got 30 days to decide whether to keep the unit or not, but if the dropouts are going to be of this magnitude and frequency from tape to tape, I think my feeling would be to return it.


I plan to take my demo tape to Harvey Electronics in N.Y.C. on Monday. I want to see if their unit shows the same glitches at the same point that mine does. If it doesn't we know for sure it's an alignment issue and my machine has a problem. If it does show the glitches than it's more likely a tape issue and then the question is why? Gee, isn't cutting edge fun! :)
 

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Nope. ;)


Am large number of people have complained about the demo tape, including me. I asked about it with my contact at JVC and we could never get an answer back from Japan. As the customer service person who called to ask my experience with my repair, I said the US side is great, the Japan side is TERRIBLE. Sorry, just speaking the facts as I have seen them first hand.


If the mits had component output, I would probably just blow off the D-Theater and have gotten them since they have shown to play tapes better.


Dave
 

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Discussion Starter · #8 ·
gridleak, dave & others,

Have you found the number of dropouts on the concert & demo tapes to increase with time? I'm finding this with the demo tape. I started with 2 video and 1 audio glitch and I've now got about 15-20 video glitches and several more audio dropouts. Interestingly they're all concentrated in and around the N.Y. segment in the 2nd half. I guess there's so many potential reasons for this from defective tape, to tape tension problems as the tape continues it's wrap, to tracking as you mentioned. Who knows?? I'm afraid to play the first 1/2 again since that portion was perfect and I want to save what I've got left as a demo for friends. I feel like I'm in a Mission Impossible series and my tape is self-destructing. :confused:
 

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It is a fact that during the first few plays the recording on the tape demagnetizes by up to 1 db, then stabilizes and reduces very slowly over many subsequent plays.


Given that a 1 db reduction in amplitude can increase the error rate by a factor of over a 100 it would appear that either your JVC 30k is marginal with respect to error rate, or the tape as originally recorded had a lower than normal signal strength (or both)


From reports posted on this forum, it would appear that the Panasonic HD1k recorder has more tolerance for lower signals than the JVC 30k.


Lower signals can also occur due to mistracking.


PS: I have no personal experience with the JVC 30k.
 

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I have been waiting for the D-Theater tapes to ship in some quantity so we can start collecting some data to see what may be going on. I havent seen the drops on std HD tapes, but cant say that I have watched as much as I have taped. In a few weeks, or maybe days, we should start getting some good reports. So for all you folks who are getting your D-THeater tapes, am very interested to hear you reports on the quality.


dave
 

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Discussion Starter · #11 ·
cymro,

Interesting about the correlation between a 1db signal decrease and an error rate increase by a factor of 100. Where does that info come from? I'm assuming this would be true of all magnetic tapes regardless of whether the data is analog or digital in nature. If this is the cause, then I guess you're right about a very low tolerance for error in the JVC. I had always assumed these units would have at least as robust an error correction circuit as do mini DV decks. Dropouts on these digital tapes (which are much much thinner) are very rare despite repeated playings.
 

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Ken Ross


The error rate equation is very similar, and very steep, for all types of digital recording. The signal read back from the tape is an analog signal for all recording methods - digital or analog. In a digital recorder, after some analog pre-processing (anti-aliasing and amplitude and phase equalization) the signal is digitized and then subjected to additional phase and amplitude equalization in the digital domain. The degree of analog vs. digital processing is a matter for the designer of the record/playback channel.


As for the bit error rate (BER) vs. Signal to noise ratio (SNR), the curve is extraordinarily steep for all types of signal processing and most communications text books publish these curves. I have seen curves in which a 1db change in the SNR causes the error rate (prior to error correction) to increase by up to a 1000 times. (that's not a typo, I really mean one thousand times).


A digital recorder must be designed to accomodate the weakest tapes, the effects of initial demagnetization, the weakest heads, wear on playback heads in addition to temperature induced effects and mistracking.


A digital recorder operating at the "design center" should have a "head room" of around 3db to deal with all the above variations.


My suspicion is that the design center of the JVC30k has less headroom than the design center of the HD 1k. Bear in mind that the bandwidth of the JVC 30k machine is reportedly around 50% more than the bandwidth of the HD 1k (28Mbit/sec bit rate instead of 19Mbit/sec bit rate); this places a significant additional burden on the designer to achieve a given error rate with a given amount of head room.


All tapes have dropouts; some dropouts are a total loss of signal, other dropouts are a few db loss of signal. The inherent BER of the machine combined with error correction algorithms is designed to deal with these problems.


If a reasonable number (say five or more) HD 1k's can all read a tape that none of a reasonable number (again say five or more) JVC 30k's cannot read, then it is fair to blame the recorder rather than the tape.


Of course the data posted on this forum isn't quite as definitive as that example, but based on Gridleak's results (among others), I think it is probable that the JVC 30k is to blame. Some samples of JVC 30k's are apparently operating well, but the "design center", IMO, isn't where it needs to be.


Most surprising is the inability of some of the JVC 30k's to read factory provided demo tapes.
 

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I have played the demo tape a few more times and still do not see what Ken is reporting- the demo tape still provides the best PQ I have seen on my display


I will keep looking for any problems


where do you get prerecorded DVHS tapes?


Mark:)
 

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Discussion Starter · #14 ·
cymro,

Thanks for the explanation. Tolerance for error sounds a bit scary in the digital domain, and I think you could be right about the design issues on the JVC relating to this.


Mark,

The only pre-recorded D-VHS tape I have is the demo tape that came with the machine. Unfortunately my video glitches are increasing at an alarming rate. At last count (last night) I'm up to about 25! I'm seriously thinking my unit could be stressing the tape in some way to cause this increase. It's either that or I've got one hell of a defective tape. In other areas the picture is pristine and absolutely gorgeous. :(
 

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I know of a person who got a bad deck. Would not play D-Theater tape except for being in the FF mode. He now has it back at JVC for repair.

Ken, I would consider sending it back for another unit just to make sure.


dave
 

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Discussion Starter · #16 ·
Dave,

What's your take on the reviews, by some of the attendees, of the WSR D-Theater showcase in another thread here? They don't sound anywhere near "glowing". One even indicated that many preferred one of the DVD titles to it's same title D-Theater release! I'm really shocked. As I said in another thread, with the greatly increased resolution and bit rate (compared to DVD), I can't see how the results were not far better than the initial reviews seemed to indicate. I also scratch my head when thinking of the STUPENDOUS reviews in WSR magazine about these same movies. What's going on?? Could perceptions by the WSR staff and the attendees of the same material be so radically different? To say I'm confused is an understatement!
 

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Ken, the first thing that caught my eye was the DVD up upconverted to 840P. I dont know how many folks have the equipment to either up convert to this, let along display it. So I dont think we are talking about apples and apples. For me the test is you take an average home theater setup with the D-Theater out of the box, and then take a DVD with a progessive player out of the box. This is the A/B comparsion that I believe is worth talking about. Anything else doesnt make sense because for people where money is not an issue, you can upconvert a DVD to probably 1080P and blow away a D-THeater tape.


Dave
 

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Quote:
Originally posted by h2ofun
Ken, the first thing that caught my eye was the DVD up upconverted to 840P. I dont know how many folks have the equipment to either up convert to this, let along display it. So I dont think we are talking about apples and apples. For me the test is you take an average home theater setup with the D-Theater out of the box, and then take a DVD with a progessive player out of the box. This is the A/B comparsion that I believe is worth talking about. Anything else doesnt make sense because for people where money is not an issue, you can upconvert a DVD to probably 1080P and blow away a D-THeater tape.


Dave


Upconvert a DVD to 1080p and blow away a D-Theater tape?


You could upconvert a DVD to 1 Million P and still not blow D-Theater away. Upconverting a DVD DOES NOT!!!! add any detail to it. I thought this was basic knowledge for anyone even remotely interested in this stuff.


bb
 

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Quote:
Originally posted by Ken Ross
gridleak, dave & others,

Have you found the number of dropouts on the concert & demo tapes to increase with time? I'm finding this with the demo tape. I started with 2 video and 1 audio glitch and I've now got about 15-20 video glitches and several more audio dropouts. Interestingly they're all concentrated in and around the N.Y. segment in the 2nd half. I guess there's so many potential reasons for this from defective tape, to tape tension problems as the tape continues it's wrap, to tracking as you mentioned. Who knows?? I'm afraid to play the first 1/2 again since that portion was perfect and I want to save what I've got left as a demo for friends. I feel like I'm in a Mission Impossible series and my tape is self-destructing. :confused:
Ken, this playback deterioration you describe is very unusual, and not something I would attribute to the tape alone.


I can suggest a few possibilities. The machine may be so poorly aligned that the tape edge is getting wrinkled on the lower cylinder or one of the posts. You could examine the tape surface on your demo to see if that's happening. It's not likely, but I have to suggest it because of the symptoms.


It's also possible that you've picked up some debris on one of the digital heads. Typically, when this happens on an HD1000, the symptoms are very similar to yours: increasing occurrence of dropouts and tiling in the latter portions of the tape. The reason it keeps getting worse is that debris tends to collect more debris, and as cymro explained in his excellent post, it doesn't take much to go from perfect to awful.


You're probably thinking that it wouldn't make sense for the heads to be dirty on a new machine, but I believe it would be worth it to clean the heads and pinch roller once and see if that fixes things. If the problem returns right away, then your machine has alignment or tape tension problems, and should be returned.


And now for some good news...


We watched the T2 tape last night on my system, and it was completely free of audio or video flaws. That's something I'm used to with my Panny stuff, and it was great to know that the JVC can perform that way as well.


Of the four D-theater tapes I own now, three play perfectly, and one has to be manually tracked. That can only mean one of two things: that there is a p2/p3 post alignment problem on my (brand new) machine, or a similar problem on the machine that made the "Yes" tape
 
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