Hi
wonder if any of you have noticed this problem before.
A tape I recorded during my travels last year seems to have a mosaic patterning problem towards the right hand side of the screen. Basically on playback, the affected area appears to be two or three frames behind the rest of the picture, resulting in quite bad blocky artefacts on that side of the screen. However, on frame advance the picture looks fine which gives me some hope that I may be able to recover the tape somehow. The tape gets better as it goes on, towards the end it is fine.
It's a sony mini DV tape recorded on a Panasonic DA-1 camncorder. I know there is an incompatability between Sony & Panasonic but this is the only time i've had this problem.
Incidentally I have tried playing the tape back on the camcorder itself, a Panasonic DV10000 deck and also the SOny DHR-1000. The problem appears slightly different on the latter machine.
help appreciated
Ed,
I don't think this is necessarily going to sort the problem but it may help to narrow it down a bit.
It could be that your heads simply need cleaning but as you have replayed in three different machines this is unlikely, as you suggest the problem is still there but is different in each of them?
The mosaic patern you mention is some sort of drop-out and could possibly have happened during recording, but as you say on single frame advance it isn't there I suspect the original recording is ok.
Have you replayed other tapes okay in each of these machines recently? It is not impossible for some muck to be transferred to other machines via the tape.
As for the incompatability issue I use both Panasonic and JVC tapes in Panasonic and JVC cameras and replay both perfectly in a Sony deck. I believe the issue was down to different lubricating materials but that was resolved a couple of years ago and now everyone uses the same lubricants.
Before you do anything else I would suggest you try a simple head cleaning job and test again.
Hope this helps.
Paul
I don't think this is tape drop-outs. To explain:
A drop-out happens when the oxide layer is damaged during record or playback, such that the playback machine has insufficient data rto reconstruct the picture. In an analogue system, this results in bursts of noise, in a digital system it may have many effects, but they won't happen vertically, they'll be horizontal.
In DV, the head drum has two heads, one in ncontact with the tape at any one time (i.e. the tape waraps only half-way round the drum). In 625-line ("PAL") systems, there are 12 sweeps of the head across the tape to make one frame. In 525-line (NTSC) there are only 10 sweeps. Each sweep of the head contains the data for the reconstruction of a horixontal slab of the picture, exactly 1/12 or 1/10 height, full width. So any drop out is going to affect one or more sweeps and appear as horizontal blocks of problems, fiull width.
I've had this with two tapes, when a head clog occurred during recording. Alternate sweeps were black on replay, this means that one head of the pair was clogged with dirt. The effect lasted about 8 seconds on the tape before the dirct was ground clear by the normal recording action. So I lost 8 seconds of recording.
If you're getting problems only down the right hand side, I would suspect the drum alignment rather than dropouts. Imagine that as the head sweeps across the tape, it's correctly placed at the start of the sweep, but the drum angle's wrong so it gradually slips off track as it progresses across the picture. Data will be gradually lost, from left to right, so you'll see block artefacts only on the right side of the picture. the effect may get better or worse with changes of temeprature because the drum angle's pretty critical. Since your problem happens only when the tape is moving and not when stationary, they drum angle seems to be just on the edge of being right, i.e. it isn't far
off right.
So, what to do about it? Take your camera to a reputable dealer with repair facilities, show him the effect and see what he says. He may be able to find another DV device that will play it, so you can clone the tape for use. He should also be able to offer you a service deal to check and realign the drum assembly.
Anyway, that's what I'd do.
Alan's explanation misses one vital ingredient - the picture content is split into blocks that are 'shuffled' before going to tape. Any partial drop-out will thus be randomly spread over the picture.
The drop-out error concealment does use the previous frame content, but this obviously cannot relate to a long term error such as a head clog. It is more likely to be an error that puts the signal on the threshold of an acceptable level. This could be head wear or perhaps a mechanical misalignment.
Thanks for the replies so far.
I have tried the head cleaning tape, it makes no difference. Neither the camcorder nor my two DV decks have a problem with any other tapes it is just this one, and it's not the tape it is just the section recorded on the one day in question, because immediately after that on the same tape there is another recording session which plays fine. The fault is exactly the same on the DA1 camcorder and the DV10000 deck. The symptoms are slightly different on the DHR-1000.
I think it must be an alignment problem but why does it play okay on frame advance!?? Infuriating!
Hi
You say that you have cleaned the heads - this will make not alter the already recorded tape - have you tried re-recording some footage and see what the results are?
Perry, the evidence of my own recordings is that each sweep of the head across the tape records one sweep across the frame. That plus the specifications. I accept that I've never seen an error cause blocks at one side of the picture though.
I had exactly the same problem with my Sony MiniDV tapes (this with a Sony camcorder). I have 4 Sony tapes and *tons* of panasonics and the Sony tapes have all shown this fault (I no longer use them). The RHS mosaics are usually accompanied by a 'click' on the audio track (but not in sync).
Since the footage on some of these was quite treasured, I got around it by capturing the footage in slomo (camera running slower) and the mosaics went away - you can then return it to normal speed in the edit.
I've never seen this problem since I've been using Panasonic tapes.
Good luck,
Adam
Yes Adam, I had thought of doing that - not sure if it's possible on my system but hopefully I'll find a way to do it!.
BTW audio distorts when played back on the DHR-1000 but it's pretty much okay on the Panasonic machines
thks
Alan - yes, clumsy English on my part. The data block shuffling is restricted to within the part of the picture relating to each head pass, which as you say is one twelth of the frame. The point is that the left and right sides of the picture are not directly related to the position of the head on its track.
[This message has been edited by PerryMitchell (edited 03 April 2002).]
OK Perry, but the symptoms still look like head tracking to me. I was a little sloppy in wording as well, I didn't mean the progress linearly across the tape, only that those on the right are more likely to relate to data blocks on the right of the tape, it's a general thing rather than a precise mapping.
Anyway, if the tape plays properly in still mode, and in slow motion, the only difference can be head tracking, and that's drum angle. It has to be down to alignment in the recorder.