mth@ihnp1.UUCP (M. Horbal) (03/13/86)
Can any of you video wizards help me? I presently have two VCR decks, a Panasonic VHS, and a Sony Beta, and am interested in making copies of tapes from one to the other. Neither of the VCR is top of the line. I recently made a few copies (beta->vhs) with less-than spectacular results, although I used the highest speed. The symptoms are a loss of sharpness, and what I would call a slight "paint-by-numbers" effect, where adjacent areas of similar color seem to blend into larger "blotches" of a uniform color. This is especially evident on people's faces, etc. Now the questions: 1. What tape should I be using to get the best quality possible, and does virgin blank tape improve results? 2. What do "video-enhencers" at al do, and can they help? My better judgement says that you can't make something out of nothing, but ... Does anyone make a decent one? Any idea how much $? 3. The Sony does not have video or audio inputs, so the output from the Panasonic would have to be be modulated onto a VHF channel, e.g 3. I am assuming that I can still record on the Sony by connecting it to the Pansonic and pretending that it's a TV (TV/VCR switch set to VCR on the Panasonic). Assuming no losses anywhere else, how much would this extra modulation affect the quality of the copy? 4. Assuming the above can be resolved, which copy direction is preferable, beta->vhs, or vhs->beta? 5. Any other suggestions? Thanks in advance. Feel free to respond either via this group, or directly. -- Mark T. Horbal IH1b230 ...ihnp4!ihnp1!mth (312) 979-3425
MRC%PANDA@SUMEX-AIM.ARPA (Mark Crispin) (03/16/86)
Mark Horbal -
The symptoms you describe are referred to as "timebase
errors", and are an unavoidable fact of life when you do
videocasette (3/4" and lower) copying. The problem is caused by
the techniques used to fit the video signal on the tape. A video
signal requires much too much bandwidth to fit on anything less
than 1" reel-to-reel videotape (many broadcasters still use the
ancient 2" format, but that is rapidly becoming extinct). With
videocassettes, the video signal is heterodyned to a lower
frequency and recorded on the tape. It is then heterotyned back
up on playback. Unfortunately, this procedures destroys some
rather precise mathematical relationships between the video
signal and the horizontal sync. Also, the VCR does not
necessarily play back the tape at exactly the same speed as it
was recorded -- that is, you get slight playback errors simply
from the normal wowing characteristics of tape.
The result is a video signal that is "close, but no cigar"
-- it cannot legally be broadcast since it does not truly conform
to NTSC. Most TV's will accept and present the picture in a
acceptable fashion -- the great acceptance of VCR's in the
consumer market shows how acceptable the pictures are. However,
the timebase error is there and it will accumulate as the tape is
copied and copies are made of the copies ("generations").
Professionals use an expensive ($7000 up) device known as a
"timebase corrector". This marvelous device reads in an entire
frame from the VCR and then outputs it, with every scan line
coming out at the correct horizontal scan rate. The price of
timebase correctors has come down, however, they are useless with
consumer equipment because consumer equipment lacks a "sync"
connection. You need to have a common sync across all of your
video equipment provided by a sync generator; consumer equipment
generates its own.
High quality videotape will alleviate some of the mechanical
causes of timebase errors, but they will never totally eliminate
timebase errors. Even more important is using the fastest speed
(Beta II or SP); the better the original the better the second
generation. A U-Matic (3/4") original will do even better.
"Video enhancers" are a cheap (although not always
inexpensive) consumer video product. They work by adding noise
to the picture to reduce the jarring effects of the timebase
errors. When the timebase errors are relatively minor, they will
improve the appearance of the overall results. I have found
enhancers to be useless with Beta (see below) but almost
essential with VHS.
The copying using the VHF inputs is known as "RF copying"
and is something you want to avoid unless you have no choice
(e.g. no video inputs). You will get playable results, but they
won't be as good as a direct video copy. I think in general
people overstate the case; video copying will not deliver a
"perfect" copy -- it will still appear quite flawed on a good
monitor. RF copying will not deliver an "unusable" copy, merely
a poorer copy.
Now, as for the copy direction. To be brief, the preferred
direction would be VHS => Beta. To be verbose, read on:
I have Beta, U-Matic, and VHS equipment. Repeated tests
have shown that copies in which VHS is the *destination* have
significantly more timebase errors (and at times audio wowing!)
than copies in which Beta or U-Matic are the destination. It
doesn't seem to matter much whether the source is Beta or VHS.
Copies from Beta or VHS to U-Matic look quite good (virtually
undiscernable from the original on a 25" monitor), and copies to
Beta or VHS from U-Matic show slight improvement (although not as
much as you might expect) over Beta or VHS source copies.
In all cases, a VHS second generation produced the worst
results. This test was done with a wide range of VHS VCR's in
tests arranged with rabid VHS fans using all of their video
stabilizers and enhancers, etc. At no time did a VHS second
generation look as good as a Beta one.
The conclusion reached by several individuals is that VHS
has intrinsically less timebase stability than Beta. This
matches the overall great effort to push consumers on to VHS.
Not only are VHS VCR's cheaper to produce (Beta's U-loading is
*expensive*!), but the movie companies et al have a strong
interest in a format which intrinsically makes copying (read:
piracy) less attractive.
Professional VHS VCR's don't seem to have this problem, but
that equipment costs *big* bucks. Just about the only places I
know that use pro VHS stuff are cable and instructional (e.g.
Stanford ITV) places. Broadcasters and producers all use 1",
U-Matic, and Betacam (Beta at 6 times the speed of Beta II).
-- Mark --
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