On Thu, 27 Jul 2000, Hársfalvi Levente wrote:
> Richard, your results, as usual, lite a lamp in my head again :-). You
> then probably can deduct the answer for the well known feature of the
> TED - by selecting some very high, but not the same frequencies for the
> TED oscillators, it is possible to get finer output voltage level steps
> that can be used for playing digi sounds, achieving almost 5 bit quality
> ('logarithmic' scale :-), finer steps at the start). I can give you an
> example code or you can also examine my SID music converter routines
> (most of them make use of this feature).
I'd like to see this code; it would give me some clues as to what other
combinations to try when quantitatively examing the TED digital SND
output.
> Also, a lamp... never heard of anyone else seen a 6561E. I have one (but
> some parts should be broken in it :-( ).
I have some 6561Es. I think they run hotter than 6561-101s.
> I don't know if there is a difference in the resolution of the PAL and
> NTSC VIC's, but one thing is for sure: the PAL VIC-I's implementation of
> the PAL color encoding could be called anything but something proper.
> PAL's spirit is in the phase-inversion of every odd and even scanlines
> color signal, but the 6561 doesn't seem to do anything like that at all.
> Once I wrote a testprogram that filled the screen with rasters, turning
> on a color in every odd and black on every even lines. Switching between
> 'parity', I got very different colors. (I could only fill the screen
> with a continuous tone if I set different color code for even and odd
> scanlines - yes, it was possible anyway :-)).
That's the odd and even lines exhibiting colour differences *precisely*
because of phase differences in opposite directions. When you sum two
lines like that in a PAL-D delay line / mixer network, you get the
original intended colour. If the two colours on alternate lines were the
same, then there wouldn't be any phase errors and there would be no need
for PAL at all. But I think the 6561 VIC-I produces phase-inverting
colours that are not exact phase inversions of each other. That doesn't
matter, because PAL automatically 'corrects' this and produces the same
overall colour every time.
Most of my studies of the VIC-20 video output have been hampered by the
lack of S-Video and my dislike of composite displays. Once I disconnected
the colour pin and was amazed by how clear the pure luminance / sync
signal was. One of these days I'll attach a normal C64 modulator & video
socket board (probably cut out of a real C64 motherboard!) to a VIC and
get proper S-Video.
Richard
--
Richard Atkinson
Software Engineer
Tenison Technology EDA Ltd
http://www.tenisontech.com/
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