Reply To: Pre ADC Gain Controls

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April 13, 2018 at 5:58 AM #20747
James-F
Participant

    Actually, these consoles were designed to work on a CRT which has quite large input voltage tolerance before clipping on all inputs, so the effect of higher input levels is exactly like raising the Contrast control on the CRT, definitely not clipping.
    There is no “root cause for clipping” when playing on a CRT which the consoles were originally designed for, that’s is why I’m against modifying the original hardware.

    Thank you again for considering including this in the next firmware.
    Will it be merged with the main ossc code on github?

    Input (analog) to output (digital) mapping equation for the OSSC:
    (0.714*1.3)*(1+(26/256))
    0.714 peak input voltage.
    1.3 (default in OSSC) coarse gain (0.5-2.0).
    26 (default in OSSC) fine gain (0-255).
    Pre ADC input level (0.714*1.3) should be less than 1.0 to prevent clipping in the digitization stage.
    Total result should be exactly 1.0 for proper mapping to 0-255 digital.

    1Chip SNES consoles output 0.8V stock.
    Video Level Specification is 0.714V.
    Thought I should include that here for people to understand what’s going on.