simper_eq bugs

[Tremus]

Bug 1: The high shelf cutoff moves when boosting / cutting

SOUL/source/soul_library/soul_library_filters.soul

Line 1532 in 2f8f74e

let g = w / sqrt (A);

Solution:
let g = w * sqrt (A);

Bug 2: The bell filters quality is not symmetrical when boosting / cutting

SOUL/source/soul_library/soul_library_filters.soul

Lines 1574 to 1578 in 2f8f74e

	c.a1 = 1 / (1 + g * (g + k));
	c.a2 = g * c.a1;
	c.a3 = g * c.a2;
	c.m0 = 1;
	c.m1 = k * (A * A - 1);

Solution:
k = 1 / (A * clamp(quality, 0.01, 100.0));

NOTE: The bell filter is the only filter that uses a different k

Source: https://cytomic.com/files/dsp/SvfLinearTrapOptimised2.pdf
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