Before digitzing 100's of family tapes I wanted to get it right so have been testing the different output captures from a JVC HR-S7600 (PAL region).
TBC ON/OFF, DR, Edit or Auto, e.t.c you all know the drill. I used 4 tapes to test- 2 commercial, 1 TV broadcast, and 1 home shot video.
The TBC ON really helps all the captures, as is recomended by the guides here. But I did come across a commercial tape that at various points during the 2 hour capture had jumping jitter when TBC was ON.
The general advice in these cases is to use another VCR like the Panasonic, and if the problem still persists to then use an external TBC/Frame sync device. But in hours and hours of reading these forums (and digitalfaq) I did read someone say jitter can be reduced by doing chassis isolation.
As one of my other crazy hobbies is high end audio, I had on hand a 2" maple spiked isolation platform, which is highly regarded among analog turntable fanatics. I did another TBC-ON capture with the VCR sitting on this platform, and now all that jitter is totally gone.
See the results for yourself. I spliced together 4 bad jittery scenes, total of 45 seconds. And repeated it from 3 different captures all with TBC ON.
jvc-tbc-(original-stutter-jitter) - This is the original capture with TBC on. (It looks bad, but the other 95% of the capture was fine).
jvc-tbc-(video-calibration-on) - This is another capture with B.E.S.T turned on, which apparently is labelled 'Video Calibration' in NTSC territories. This feature helped - it removed about 30-40% of the jitter across the capture as you can see, but that still leaves a lot.
jvc-tbc-(isolation-platform) - This is the final capture done with the VCR on the isolation platform. All jitter gone. (B.E.S.T/Video Calibration is turned off in this capture).
I know this is only 1 example, and the isolation fix may not work in all cases, but this points to the JVC TBC circuit being highly susceptible to mechanical induced chassis vibration. My workbench desk is sturdy as it is now, but real isolation is obviously required. I have not even begun to investigate the effect on putting isolation under the VCR itself. You could use footers or even go insane with something like Stillpoints, which I own for my audio system.
I am new to all this VCR capture thing, but thought you all may get something from this test, because I have not come across any threads of people investigating the effects of mechanical vibration and TBC, or of isolation platforms and VCR's in general.
[Attachment 58590 - Click to enlarge]
+ Reply to Thread
Results 1 to 20 of 20
I think this also could explains why the higher end JVC models are reported to handle jitter better, because the chassis is more substantial and damped on the 9600/9700 and SRW5 models ?
Here is an exact frame comparison. All settings here were EDIT mode and nothing else turned on.
The top frame is from TBC OFF.
The middle frame is TBC ON.
The bottom frame is TBC ON and ISOLATED.
[Attachment 58591 - Click to enlarge]
While I agree with the fact that physical vibration can alter video drum stabilization and lead to jitter like tapping on the VCR with your hand, The kind of vibration from surrounding air and leaked ground vibration from passing by vehicles or walking in the room does not affect the performance of a VCR like it does to say a turntable for two main reasons:
Reason 1 is because video signal is not recorded directly to tape, it is modulated into a FM frequency in the MHz range called RF and altering the video signal requires a serious disturbance to the RF signal, like knocking or hitting the VCR (not recommending doing so), another example of that is FM radio, you can loose some of the FM modulated signal and you can still get a crisp clean audio before you start getting light static, It kind of behaves like digital where you get a picture or you don't.
Reason 2, Video drum motor has a precise feedback motor torque and speed control, The motor control IC can compensate for a small percentage of torque and speed fluctuation before it starts affecting the speed accuracy, Not to mention that the drum is a heavy piece of metal and once it locks on a speed it is dead solid unless you knock or tap on the VCR.
The other thing is B.E.S.T has nothing to do with vibration, B.E.S.T for video in a nutshell is equalization for audio tapes, B.E.S.T IC analyses the tape formulation by recording few seconds of RF signal on it and reads it back, Based on the results obtained it adjusts the current supplied to the heads' coils to compensate for the type and condition of the tape being used for either recording or playback, It has absolutely nothing to do with vibration and signal timing.
While it doesn't hurt to put that nice piece of table underneath your VCR, the supposed visual improvement is just a placebo effect in my opinion except in the B.E.S.T case, If there is any differences in your sample with table on it has to be due to other factors like components get warm, tape tension or slack that is not consistent, try several repeated tests to find out for sure.
Last edited by dellsam34; 26th Apr 2021 at 00:23.
Forgive me if I misunderstand but the isolation pads/legs/cones on high end audio equipment are for preventing external vibrations being picked up aren't they? For example, to reduce vibrations from a table top reaching a record stylus.
Isolating the device that actually causes vibrations, like the head and tape motors would make it more likely the whole deck would vibrate so if it is indeed the cause of jitter it would become worse, not better.
I am doing some brand new captures right now to recreate this effect, and putting the VCR on the wood desk itself instead of leaving the soft packaging cover underneath.
B.E.S.T IC analyses the tape formulation by recording few seconds of RF signal on it and reads it back
Each time I play a tape with B.E.S.T. on, when the video starts the B.E.S.T. spy flashes indicating some activity; but the real recorded signal is not affected (otherwise after many readings there should be some corruption)
Is the isolating platform wood, plastic or metal? Are there any mains leads near where the VCR is positioned? (including mains wires in the walls - e.g. is it near to a mains socket and either at the same level or immediately above or below it?) Is it possible that the platform is either shielding the VCR from a local source of interference or just moving it far enough away that it's effects are not so noticeable? (Inverse square law and all that.)
The photo above shows the VCR sitting on the bench on either a piece of paper or material, was the bit of paper/material there when you did the captures? If it was, is it possible that it was partially blocking some of the ventilations slots in the bottom of the VCR (if it has any) and causing the VCR to run a bit hotter? (I had something similar with my two Liteon DVD recorders, and just increasing the airgap under the recorders by even just the height of a CD case would cure the problem.)"Well, my days of not taking you seriously are certainly coming to a middle."
CALIBRATION / BEST causes more issues than not.
It rarely works as you'd think.
Heat wouldn't care this.
LiteOn DVD recorder is way different issues.
This whole thing is odd. Reminds me of superstition. Holding your mouth a certain way makes X happen. Doesn't make sense.
If I understand correctly, what's been posted is tape playback #1, #2, and #3.
Did you go back and verify that the settings used with playback #1 still produce the "stutter/jitter" upon playback #4 without isolation?
What I'm getting at is that simply playing and rewinding the tape can produce some mechanical differences.(Formerly vaporeon800)
I just did 4 new TBC captures. The first 3 - on foam matt, on hardwood desk, on isolation platform. The jitter was now totally gone from all captures.
I thought bugger, I have got this all wrong, the isolation makes no difference, and I messed up the initial captures somehow.
But these 3 new captures were all only of the 8 minute segment that contained the 4 scenes I am analysing. The previous captures were all longform 2 hours. So maybe as the TBC circuit heats up, it starts to play up on this unit? And I noticed all my previous 2 hour captures, no jitter/stutter was present in the first 1/2 hour of each capture.
So I just did a new capture, on the foam matt as before, long form. The jitter is now back at the exact same points, starting about 40 minutes into the tape.
So it looks like possibly a heat issue, and lifting the VCR off the foam matting onto the platform alleviated the heat issue allowing the TBC to work better. This may be just specific to this unit being old and faulty.
I will try another capture on the foam matt, but this time with the case lid off, for maximum air.
EDIT - Lid off and now no jitter on a long capture. Also I tried lid on again, and jitter returned.
So I was wrong about the isolation. It's heat that seems to cause the TBC to fritz after an extended period of use (on this unit).
Question, which part of the player does the TBC? There are 2 circuit boards parallel to each other at the back of the unit.
Last edited by agisthos; 26th Apr 2021 at 14:25.
agisthos, are you saying your 7600 has been sitting on that piece of foam packing sheet the entire time prior to experimenting with the turntable platform? Including the time covered by your other thread about TBC judder?
If so, thats... problematic. Why on earth would you let it sit during active use on soft heat-insulating material like that? As an avid audiophile, presumably you must have known that would be terrible for circuit ventilation.
Were you just so stunned by the mint condition of your newly-arrived 7600 that your fear of scuffing the bottom overcame your practical electronics experience?
Not that I would have been terribly surprised if the isolation platform really did improbably solve your judder issue via vibration damping: these JVC VCRs (and the equally ridiculous Panasonic AG1980) are the most histrionic boxes of hypersensitive glitch-ridden BS ever foisted on the paying public. They misbehave at the slightest provocation (weather, astrological arrangements, house settling, planes flying overhead, pothole being filled three blocks away). I live for the day my years-long VHS transfer project is finally completed, and I can gleefully toss each one of these sadistic diva VCRs out my attic window onto my concrete driveway.
Anyway, Heat problems could be an indication of failing capacitors, You know the old trick, an air spray can and a heat gun can pinpoint the faulty area by spraying component directly or blowing heat on them.
Last edited by dellsam34; 26th Apr 2021 at 17:25.
I thought that was the one. It had some kind of metal shield on it as well.
Does it plug in/out of a slot on the mainboard, or is it soldered into the mainboard? If its the later.... that makes things a bit more PITA.
Look up your exact model number service manual, it should tel you how it is mounted to the main board.