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/ - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail firstname.lastname@example.org.
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