Den Thu, 31 Aug 2017 23:58:48 +0200 skrev email@example.com: > > > On 2017-08-31, at 23:19, Mia Magnusson <firstname.lastname@example.org> wrote: > > > > Well, the slightly off sync frequencys (and being non interlace) > > would require a TBC to correct but the levels, impedance and the > > timing difference between chroma and luma could easily be > > corrected. Also any improper sync signal (lenght of pulses, > > wafeform e.t.c.) could be corrected. > > When I was pushing that, I was almost sure everything could be > handled and corrected. The eventual show-stopper was when I realised > that odd and even fields are actually of different duration and there > is no way to make VIC-II generate make every other field > longer/shorter. Well, as long as you can store about one line you could tweak the clock frequency of the computer so that it produces 624 lines every 1/25 second, and then just insert one extra line on every other field. > > But as the sync frequencies is non-standard there is > > probably not much use for such correction, as all the non-standard > > stuff anyway works on most displays (except that the chroma-luma > > delay gives a worse picture quality than what is possible to > > achieve). > > The non-standard C64 signal works on analogue displays as they are > both analogue driven and also (in big part because of that) > accommodate much wider differences. The current circuitry rarely > works acceptably well with strongly non-standard signals like those > from the 64. > > > For some reason the decoding process in a TV anyway needs a delay. > > It's likely that the s-video standard were set to make a S-VHS > > player as simple as possible, i.e. bypassing any delay that's > > needed for a VHS to do composite -> separate chroma/luma -> FM > > modulate luma and frequency shift chroma -> record to tape, > > playback from tape -> FM demodulate luma and frequency shift chroma > > -> combine luma and chroma. > > > > So therefore it makes sense that the signals could have different > > timing specs for composite v.s. s-video in general. > > I /think/ the difference in the delays in the decoders are caused by > different signal paths, not by the difference in the specs of CVBS > vs. Y/C. The delay lines are needed for other reasons. > > To make sure (I believe so but am happy to verify) I can take a test > signal generator (still should have a higher-end Fluke somewhere) and > put both on the scope to see if there is any noticeable difference. > You said you estimated the delay you wanted to introduce. What would > that be? In other words - for what time difference am I supposed to > look? It would be interesting to see what you get with a test generator compared with a C64. My experience is that composite video is good on C64 but S-video is about two dot clock cycles off, with chroma coming later than luma. > > Could it maybe be that the professional displays compensate for > > timing issues (by looking at the timing of the color burst v.s. the > > sync pulses)? > > No, the exact opposite is more true. They show things "as they are". > That's the one of the main reasons for using them in studios in the > first place. I would had assumed that they had two modes, "technician" and "producer/audience", where "technician" would show all errors but "producer/audience" try to show a good picture. (Of course the modes would have other names). > > In practise the light green border on the C128 default screen has a > > white stripe right next to the right edge of the visible area, and > > there is corresponding bleed from the green border onto the text > > area to the left of the visible area. The white stripe is about as > > wide as two pixels, which is why I'm guessing about 30 metres cable > > delay would probably make the picture better. (Sorry if I'm writing > > the same stuff all over, I tend to forget what I've already told or > > not :) ) > > Ah, now I forgot what you already wrote before - so that's the timing > difference you're looking at - two pixelclock cycles of a C64 PAL > signal, right? Yes, about two pixeclock cycles judging by my eyes on my modern TV. I should bring up the old CRT TV and see how it looks on that too. -- (\_/) Copy the bunny to your mails to help (O.o) him achieve world domination. (> <) Come join the dark side. /_|_\ We have cookies. Message was sent through the cbm-hackers mailing listReceived on 2017-09-02 03:00:20
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