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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions. |
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8th Apr 2015, 12:24 pm | #1 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Playback of degraded VHS. Replacement sync insert.
I remember reading an article in the Practical Television magazine about various methods of improving the playback quality of degraded VHS video tapes.
An idea suggested was to employ the head control pulse to insert new frame sync pulses, these would replace the recorded frame syncs. I've never tried this myself but I'd reckon this would be a viable project. The 50Hz CTL pulse is almost coincident with the field sync pulse so no timing problems. DFWB. |
8th Apr 2015, 3:19 pm | #2 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,947
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Re: Playback of degraded VHS. Replacement sync insert.
Didn't a lot of higher spec VCRs do this?
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8th Apr 2015, 3:22 pm | #3 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,846
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Re: Playback of degraded VHS. Replacement sync insert.
Is this "timebase correction" or am I barking up the wrong tree?
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8th Apr 2015, 4:24 pm | #4 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
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Re: Playback of degraded VHS. Replacement sync insert.
You could play the tapes through a DVD recorder set to pause - the sync correction
can provide amazing results. Various devices were made to "sharpen" the picture using hf boost, but these usually ended up with image edges having an "outline" effect. |
8th Apr 2015, 8:35 pm | #5 |
Hexode
Join Date: Jul 2009
Location: Mablethorpe, Lincolnshire, UK.
Posts: 286
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Re: Playback of degraded VHS. Replacement sync insert.
Nick, this is indeed timebase correction. I got hold of just such a beast a couple of months back and looking on the scope, it does an excellent job of replacing the sync pulses. It also provides controls for video and colour levels, as well as noise reduction (which is very good) and drop-out compensation (which isn't so hot).
Some professional machines had all this built in. I would say it would be well worth trying and a very useful project. Mark. |
8th Apr 2015, 8:53 pm | #6 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,846
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Re: Playback of degraded VHS. Replacement sync insert.
Thanks Mark.
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8th Apr 2015, 9:35 pm | #7 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Re: Playback of degraded VHS. Replacement sync insert.
Certain ITT video recorders had ASO, not sure what the abbreviation means, but nevertheless it really improved the picture quality.
Was a ASO a Sanyo development? DFWB. |
8th Apr 2015, 11:02 pm | #8 |
Nonode
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 2,819
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Re: Playback of degraded VHS. Replacement sync insert.
I have a JVC VHS-C camcorder with time base corrector built into it, works quite well!
Regards, Lloyd |
9th Apr 2015, 12:40 am | #9 |
Moderator
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Re: Playback of degraded VHS. Replacement sync insert.
I think JVC were quite keen on this and incorporated it into a lot of their models.
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9th Apr 2015, 9:36 am | #10 |
Octode
Join Date: Jan 2013
Location: Barnsley, South Yorkshire, UK.
Posts: 1,517
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Re: Playback of degraded VHS. Replacement sync insert.
The drop out compensator will only work when an rf feed from the head amplifier is available. TBCs offering DOC almost always had a BNC or similar input socket into which off-tape rf was fed; the TBC detects the loss of rf due to the dropout and then repeats the video line above which it has in store instead of just showing the noise/shash.
Another 'proto' TBC is known as a 'proc-amp' or processing amplifier (to give it its Sunday name) and the related line clamp amplifier. These did the sync re-insert and reblanking but without the re-timing and storage capabilities. |
9th Apr 2015, 10:19 am | #11 |
Heptode
Join Date: May 2009
Location: Birmingham, West Midlands, UK.
Posts: 708
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Re: Playback of degraded VHS. Replacement sync insert.
Certainly in a professional situation such as a studio where you have much more stable sources such as cameras and caption generators a TBC was a must for the VTR and especially helical scan VTRs.
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9th Apr 2015, 12:36 pm | #12 |
Octode
Join Date: Jan 2013
Location: Barnsley, South Yorkshire, UK.
Posts: 1,517
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Re: Playback of degraded VHS. Replacement sync insert.
As 'Charlie' says helical scan VTRs, though amazingly stable for a mechanical device, couldn't possibly maintain electronic timing standards over the length of time of a TV field (1 head transit). The first generation professional VTRs recorded only 16 lines per head transit and could, just about (in the B&W era) be stable enough to sync up with a stable electronic source without a TBC. Helical scan machines which include VHS, Beta, U-matic etc couldn't be used in a fadeto/mix to/wipe to situation until TBCs became available although, in desperation, the most stable could be 'cut to' or 'switch lock' as RCA used to call it.
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9th Apr 2015, 6:29 pm | #13 |
Hexode
Join Date: Jul 2009
Location: Mablethorpe, Lincolnshire, UK.
Posts: 286
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Re: Playback of degraded VHS. Replacement sync insert.
Thanks for the info. I did find out about feeding in the RF direct from the head and luckily I have a professional JVC machine that has this output on the back. Even so, I don't think it is that brilliant. I can see it working if I pause the machine and move the tape to produce a noise bar. It is adjustable, but if I go too far, it makes things look even worse.
I have noticed that it does not like working with pre-recorded tapes. I presume the dreaded Macrovision is playing havoc with the circuitry. Mark. |
12th Apr 2015, 10:18 pm | #14 |
Octode
Join Date: Mar 2006
Location: Watford, Hertfordshire, UK.
Posts: 1,270
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Re: Playback of degraded VHS. Replacement sync insert.
One device, no longer made but may be available at some time on an auction site is the ACE.
http://www.gthelectronics.com/featurec.htm
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