White-pumping also by non-SCART gear?

[Ghitulescu]

The other thread of mine, 3 months old and with some 1k5 visualisations, was not interesting at all apparently.

There are some 10 years since a user, also of doom9, discovered the "white pumping". Also nothing else than an endnote in the history of analogue playback and capturing. For those not knowing what has been reported, see this entry in another forum, also with some video -> https://forum.videohelp.com/threads/...e9#post2685720 .

Essentially, there is an "echo" in the video outputs (S-Video was particularly tested) but the SCART signals of the same device were unaffected.

This issue has been extensively discussed in the German forums, but went, again, unnoticved in the rest of the world.
Maybe the "rest of the world" thought that this an European thing, since SCART was involved.

I think they are wrong. I think that the SCART, which required a certain configuration, was a correction, not an error. My guess is that all others, non-SCART, are or may be faulty, exactly the same as the Hosiden outputs by PAL gear.
Anyway, the lack of buffering is the main reason why, in audio, the quality of interconnect cables counts. And also is the culprit here - the "echo" appears to be caused by the capacitor which is the only "buffer" for S-Video (the SCART has a true buffer instead, because it's direct DC-coupling). Since the costs of a capacitor is much lower than that of a true buffer, the premium devices (Panny E20, HS2) did not suffer from this, whereas the others did (EH, ES series).

Of course I cannot prove this, as living in the middle of the PAL-Continent is difficult to find NTSC-pure gear.

Maybe someone can test this issue...

[Sharc]

In my experience (PAL) the "pumping" is caused by the instability of the DC-level restoration of "black":
- SCART outputs (Y-wire) on the PAL Pannys which I tested are DC coupled with a restored rock solid "black" level, clamped at a fixed voltage. So the capture device receives a stable signal.
- The S-video on the Mini-DIN/Hosiden Y-wire is AC-coupled (capacitive coupling), means the "black" signal level fluctuates up and down according to the average signal level of the picture dependent luma+sync. So the task of restoring and clamping the "black" level is entirely left to the subsequent capture card; same for AGC. Quality of the DC restoration and AGC action depend on the capture device.

[Emulgator]

Histogram("...\Panasonic DMR Vergleich S-Video Out- Scart S-Video Out.mkv")
delivers stable blacks here, around 16..18.
Whites are pumping, but I see it on both output panes, S-Video and Scart.
I even mean to see the same rhythm, just phase shifted.
Normally I would expect a smooth AGC reponse, depending on AGCs involved max 1 overshoot.
What if bogilein's source was the culprit? Did he play an instable recording of a S-VHS tape into the Panny DMRs
and some AGC helped ?

Capture Setup:
SVHS VCR Hitachi S390 (no TBC) connected with a S-Video cable to the front inputs of the respective Panasonic DMR.
Then output once via S-Video into the capture card Hauppauge USB 2 Live.
And once via the S-Video output of the Scart adapter into the Hauppauge USB2 Live.
The whole as SPlitscreen-Video to compare the outputs.
Everyone should make up his own mind whether it bothers him or not.

Just for a coarse comparison I looked up the schematics of 2 Panny S-VHS HS-950 and AG-7650 here: Both signal paths are DC-coupled.

[Sharc]

The darks on the S-video out of the said Pannys (ES-10, ES-15, ES-20, EH-65, EX-77, EH-495) is clearly pumping (bouncing) 2....3x here after each transition white->dark, using the waveform monitor (or the eyes).....
The white is continually fluctuating a bit (unless it is clipped in some of the tests), but I think this is on the tape.

[Ghitulescu]

Originally Posted by Emulgator

Just for a coarse comparison I looked up the schematics of 2 Panny S-VHS HS-950 and AG-7650 here: Both signal paths are DC-coupled.

Indeed, that was the second point of my initial thread (I avoided on purpose the use of word VCR or DVD-Recorder, not to bias/channel the answers):

• are other manufacturers, than Panasonic, affected??
• are other devices, other than Panasonic DMR-xxx, affected??

I think yes, since it's hard to believe that a manufacturer would change the schematics so drastically from one product line to another, when the same goal (interfacing to eg TV, beamer etc.) is sought. Maybe premium models have a better (more expensive) interface, across all product lines - but this is all.
It's also hard to believe that less expensive products would employ better interfaces than the more expensive ones (Panasonic, JVC, Sony - essentially all manufacturers recommended as players in capturing guides - demand more money than others, like Orion, Funai and stuff).

Originally Posted by Emulgator

What if bogilein's source was the culprit? Did he play an instable recording of a S-VHS tape [...]

Well, analogue is actually a tale of statistics - no identical results over repeteadly runs of the same material - yet, it is hard to assume that the Hitachi S380 provided such different results, as these are clearly shown (HS2 vs. eg ES20).



To me, this appeared to be a general issue, concerning all devices that do not have DC-coupled outputs. This is why I wondered why it didn't catch the attention, although reported many times...
In any case, this is worrying, especially when one spends fortunes on hardware for getting the best, only to find out that s/he can't rely on the proper interfacing them.

[Sharc]

One should evaluate all this together with the capture (receiving) device, because different capture devices (cards, dongles, receivers) act differently on AC-coupled 'Y+sync' signals.
From an engineering point of view DC coupling between equipment is a crime, but for video it takes the burden away from cheap capture devices of restoring the DC-level stably and correctly, as some don't behave nicely with the dancing AC-coupled signals. Choose your poison.