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Re: STAR RIDER 19 FEB 2014 PROGRESS :)
02/21/14 08:10 PM
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> > In plain English: I think it's absolutely *possible* to decode NTSC better than
> many
> > of the original players and monitors did. I said nothing about if it's desirable to
> > do so in MAME.
Note that the current video in MAME was decoded from composite to YUV using a fairly sophisticated ATI video capture card. Results aren't likely to get dramatically better, except perhaps with some clever use of DSP/filtering to clean things up.
> Were I to attempt this again (and I intend to), I plan on using a 30 MHz ADC instead
> of a 15 MHz (since I think 15 is too slow to get the full resolution), still probably
> 12-bit samples, and still using an FPGA, but this time I want to output the data over
> ethernet to a desktop PC so that I don't have to worry about write bandwidth.
15 MHz is sufficient to fully capture the NTSC output of the player. (Old broadcast quality gear that captures composite digital uses 14.32 MHz, four times the color subcarrier frequency, and well above the Nyquist rate for a signal with 6 MHz bandwidth tops.)
If we're going a step further back, inside the player, before the modulated signal on the disc is separated into audio and video, then yes, 15 MHz isn't going to be enough. I think it's an 8 or 9 MHz carrier, so a 6 MHz video signal shouldn't bump it higher than 12 MHz or so, right? 24 MHz would cover this. I'm not sure how complicated the demodulation is in a typical player, so I don't know how much purer we could expect this to be.
I definitely support the gigabit ethernet approach, especially if there's any existing FPGA code that would support it. Much nicer than monkeying with SD cards!
Edited by WarrenO (02/21/14 08:11 PM)
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