[opendtv] Re: Half Truths - Was More 1080p@60
- From: Cliff Benham <flyback1@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 07 Dec 2007 20:46:51 -0500
Manfredi, Albert E wrote:
Being analog, NTSC TV has some 'slop' in the physical embodiment
of the technical specifications it aspires to.
How else would it be possible to play VHS tapes on a $30 VCR
from Woolco that uses 'rubber bands' to spin the head drum and
the capstan and still get a pretty good color picture from it?
The sync is provided in the recorded signal, not by the rubber bands!
If the rubber bands stretch or slip, if the brakebands in the mechanical
tension holdback *servo* aren't working right the sync wanders all over
hell's half acre! Watch a VHS tape over an older TV from the 1970s if
you don't believe me!
I had one of the first hifi VHS recorders, which allowed audio-only
recording. (They quickly dropped that feature in hifi VHS VCRs.)
So in my first attempt, I just tried to record audio alone, no video
input, without paying careful attention to the switch settings.
It didn't work worth a d*mn.
Then I looked at the manual, and sure enough, there was a tiny switch
behind a front cover that had to be moved. So in audio-only, the VCR
synched up to the 60 Hz power frequency.
Doubtful; it probably synced to it's internal sync. generator chip. By
the time VHS HI-FI was de rigueur, VCRS had sync generators built in and
no longer referenced the 60 Hz line. Especially those portable units
that ran on batteries or 12 VDC in the car.
Anyway, I think that if you try to send 60 fps NTSC video, you will
notice the interference that Wikipedia article talked about.
NO. You probably won't see it at all. If that were the case you would
see it when playing VHS tapes because of the jitter and instability of
such machines because they have no internal time base corrector. I don't
give lots of credence to *Wikiality*.
I've also read somewhere that even RCA finally admitted that changing
the sync frequencies by 1000/1001 probably wasn't necessary. The change
was to 'hide' the 916.75 kHz moire [caused by the CSC beating with the
4.5 mHz audio carrier] visible on early B&W sets by changing it up to
920.0455 kHz, hidden by 'frequency interlace'. It became a non-issue
after the late 50s when the older B&W sets were being replaced by newer
ones with better IF systems.
This information may have been in George H. Brown's book, 'And Part of
Which I was...Recollections of a Research Engineer'.
Bert
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