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Old 3rd September 2017, 06:54   #1  |  Link
Katie Boundary
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An unexpected property of b=0, c=1 cubics

A few months or years ago, I was playing around with different settings for cubic filters and noted that despite the "B+2C=1" rule, the cubics that gave the best overall results seemed to be at about b=0, c=1.

Today, I was playing around with filter shapes in Desmos and noticed something very peculiar: at x=1, the tangent of a raw sinc function is -1, and the tangent of a b=0, c=1 cubic is ALSO -1. This is also where both filter shapes are at their steepest. That's the reason why cubics start to look like ass beyond c>1: the filter shape gets "too steep" (defined as steeper than raw sinc) at x=1.
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Last edited by Katie Boundary; 5th September 2017 at 05:40.
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Old 6th September 2017, 04:54   #2  |  Link
Katie Boundary
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To demonstrate, I made a pretty:

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