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Cake day: June 16th, 2023

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  • For ntsc vhs players it wasnt a component in the vcr that was made for copy protection. They would add garbled color burst signals. This would desync the automatic color burst sync system on the vcr.

    CRT TVs didn’t need this component but some fancy tvs would also have the same problem with macrovission.

    The color burst system was actually a pretty cool invention from the time broadcast started to add color. They needed to be able stay compatible with existing black and white tv.

    The solution was to not change the black and white image being sent but add the color offset information on a higher frequency and color TVs would combine the signals.

    This was easy for CRT as the electron beam would sweep across the screen changing intensity as it hit each black and white pixel.

    To display color each black and white pixel was a RGB triangle of pixels. So you would add small offset to the beam up or down to make it more or less green and left or right to adjust the red and blue.

    Those adjustment knobs on old tvs were in part you manually targeting the beam adjustment to hit the pixels just right.

    VCRs didn’t usually have these adjustments so they needed a auto system to keep the color synced in the recording.














  • I’ll add that frequencies above the Nyquist point fold into lower frequencies. So you need to filter out the higher frequencies with a low pass filter.

    This isn’t just for audio but any type of sampling frequencies. For example in video when you see wagon wheels going backwards, helicopter blades moving slowly, or old CRT displays where there is a big bright horizontal line sweeping. That’s all frequency folding around half the frame rate.

    It also applies to grids in images. The pixels in a display act a sample points and you get frequency folding leading to jagged lines. Because a line segment is a half cycle of a square wave with a period of twice the length.

    When that segment is diagonal it become a two dimensional signal with even higher frequency components in each axes. This leads to jagged diagonal lines. This is called aliasing as the higher frequencies have an alies as lower frequencies.

    So when you apply antialiasing in video games it’s doing math to smear the signal along the two axis of the display. This makes a cleaner looking line.