From: mike@vm.brl.mil (Michael John Muuss <mike>)
Newsgroups: rec.video
Subject: Re: S-VHS vs regular video output
Date: 2 Sep 92 23:52:36 GMT
Reply-To: mike@brl.mil
Organization: Ballistic Research Laboratory

In article <1992Sep1.014715.17596@mprgate.mpr.ca>, ng@mprgate.mpr.ca (Steve Ng) writes:
|> I have a Pioneer laser disc player at home. It has both S-VHS output and 
|> regular video ouput. By theory, I thought S-VHS gives sharper image and 
|> better colour than regular video. However, when I compare the video 1 S-Video 
|> input (of my TV which a Sony XBR Trinitron) which is connected to the S-VHS 
|> ouput of the laser disc player and the video 2 regular video input which is 
|> connected to the regular video output of the same laser disc player, I cannot 
|> see any difference in picture quality. I am a bit disappointed since I spent 
|> $45 dollar on the S-VHS cable (a double shielded OFC cable). 

Here is something I wrote in July that didn't seem to make it out to the
USENET, but only to InterNet folks via VIDEOTECH@WSMR-SIMTEL20.ARMY.MIL:

Date: Fri, 17 Jul 92 19:24:59 EDT
From: Mike Muuss <mike@BRL.MIL>
Subject: Re: S-video input for Laser Disc player

Bill Cruce wrote:

> My advice is not to worry.  You will see a quality improvement from
> laser disc that far exceeds any difference between standard (composite)
> video and S-Video.  On my own setup which lets me switch any which way
> I choose, I have found the standard video output of my laser disc player
> gives the best picture (usually).  Other drivers mileage does vary.

It is worth noting that LD's have analog composite video actually
recorded on the disk, not separated Y/C, as is done with videotapes.
Thus, in the simple case, the issue becomes one of determining whether
the NTSC to Y/C decoder in your LD machine is better than the one in
your TV set/monitor.  In most cases, the difference is probably small.

There is an exception to this, namely, if your LD machine has a
time-base corrector (TBC) built in, where the front-end of the TBC
performs a Y/C separation before digitizing the video.  On such systems,
the TBC output will be Y/C, and in that case, by using the S-Video
connection, you bypass two processing steps, (1) encoding Y/C back
to composite, inside the LD machine, and (2) decoding composite back
into Y/C (on it's way to becomming RGB) inside the TV/monitor.  In this
case, using an S-Video connection is likely to retain much more image
quality.

My this is how the TBC inside the Pioneer CLD-91 and CLD-92 work, as
well as the LD-S2.  Since I have a CLD-91, using S-Video allows me to
avoid an extra encode-decode step.

Every time you avoid an NTSC-encoding step, you are likely to get fewer
artifacts, like dot-crawl and luminance/chrominance aliasing.

Another case where S-Video links can be beneficial are when the LD
machine and the TV/monitor are far apart.  In that case, the S-Video
signal, being composed of two lower-bandwidth parts (one per cable),
rather a single composite signal, will tend to degrade less with
distance. This degradation is usually first noticed as loss of chroma
bandwidth (color bleeding), because the color information in a composite
signal is sent at a higher frequency.

Distance is a factor for me, as I have all my line-level electronics
*behind* the sofa, and the monitor (NEC 27"), front power amps (2 *
Adcom GFA-555), and front speakers on the other side of the listening
room, 50 cable-feet away.  I send the audio to the power amps via
MonsterCable M-1000, and I send S-Video via two runs of RG-6U (0.9 dB
loss per 100 feet at 10 MHz).  The loss of audio quality over that
distance was minute (a very slight attenuation in the very high
frequencies, roughly -1dB > 15 KHz); I have not been able to measure any
loss of video quality; I get 425 "TV lines" of resolution from the LD
player to the screen, regardless of whether I use the long RG-6U cables,
or the short S-Video cable.

[ After I sent that message, Bob Niland replied: ]

> Hook your LD player to a "video" input and save the "S-video" input
> for your VCR/TV interlink (not that it buys you much there, either).

And lit me off again...

I have to take exception to the parenthetical remark:  if you have
a good VCR, and a well recorded tape, my own experience has been that
using the S-video output results in substantially better final
picture quality, both at home, and in the studio.

For myself I have verified this by connecting both the composite and
S-video outputs of a VCR to both the composite and S-video inputs of a
Microtime TX-3FIT format transcoding 4:2:2 digital timebase corrector.
I observe the output of the TX-3 on a Sony PVM-1944Q fine-pitch monitor,
fed by both the composite and S-video outputs of the TX-3. Even using
the composite path to the monitor, the image quality is *substantially*
better when the TX-3 is fed from the S-video output of the VCR, as
opposed to feeding it from the composite output.  This makes a good
test setup, as the different paths can be checked by flicking a switch,
allowing good A/B comparison.  The same results can be observed by
omitting the TX-3 and going straight to the monitor, although results
are a bit harder to judge, owing to the time inaccuracies of the signal
seeming to blur the image slightly.

The reason for this I hinted at in my previous note:  analog videotapes
are recorded in Y/C form, not composite.  Avoiding one encoding and
one decoding step (where the intermediate (composite) format is of lower
overall bandwidth than Y/C) should generally give better results.

Whenever you have the option of taking Y/C output of a VCR, do so.
At least experiment with it, and see what looks better.  Have a friend
at a local TV station or computer graphics facility record you a tape
with SMPTE color bars and the "multiburst" pattern, so that you can make
reasonable accurate judgements of your system's performance by eye.

If you have an LD player, these test patterns are on "A Video Standard"
from Reference Recordings, along with an explanation of how to use
them.  If you are at all serious about quality, at least rent this disk.

It is quite reasonable to take the S-video output of your LD player,
feed it into the S-video input of your VCR, and then run S-video from
the VCR to the monitor.  By selecting the "S-video line in" setting on
your VCR, you can watch a LD.  The only drawback to this strategy is
that you have to turn on the VCR to use the LD player.  I have my own
system wired this way, and it causes no problems, and offers one
benefit: my VCR has a digital noise reduction (NR) circuit in it.  A few
LD's have enough video noise to make the NR artifacts less objectionable
than the noise itself, so on them I just click on the VCR's NR circuit,
and clean up the video from the LD.

On the subject of purchasing a LD player...

Having been trained as an engineer, I'm perhaps a bit more of a
technophile than some.  Before I buy equipment, I spend a lot of time
judging it subjectively, and then I make measurements to see if I can
explain what I observed.  When I was preparing to buy my LD player, I
brought a 250 MHz o'scope, NTSC waveform analyzer, and NTSC vectorscope
along when I went shopping, so that I could conduct accurate
measurements.  Once I had decided on the model I wanted (I picked the
Pioneer CLD-91, because it provided fairly acceptable video quality [for
'pro engineer standards] at a price I could manage), the deal I made
with the store was that I would test the unit I was acutally going to
purchase, and if it "looked good" to me, and met manufacturers specs,
then I'd take it.  Otherwise, we would open another box and try again.

Needless to say, this operation was a bit of a spectacle. I had made
arrangements with the manager of the store *in advance*, so that the
staff was prepared for me to drag in my pile of equipment.  I came just
after lunch (their slowest hours) on their slowest day of the week
(Tuesday, I think).  Amusingly, there was a Pioneer rep from California
there that week, and he took copious notes as I announced my
measurements and made a few biting remarks.  A bit of a crowd gathered
to watch.  We were all having a good time, and I took the time to
explain to folks what each measurement was, and what it was good for. It
was not too surprising that along the way I sold two more CLD-91's for
the store, while I was putting mine through it's paces.  As it turned out,
the first carton we opened proved acceptable, and I've been very happy
with it.

[The store is Laserland in WhiteMarsh MD.  I have done business there for
several years, and I've been completely satisfied with them.]

If you take the time to educate your eyes (and ears), and shop around,
you can do very well, without spending a fortune...

	Best,
	 -Mike

	  Advanced Computer Systems
	  Ballistic Research Laboratory
	  APG, MD  21005-5066
Newsgroups: rec.video