EQ Filter Change: Butterworth swap with Bessel

Currently the EQ uses Butterworth filtering but Bessel would be a smoother and safer option.

http://www.rfwireless-world.com/images/Butterworth-Filter-vs-Bessel-Filter.jpg

Butterworth causes ripples which can exceed the original signal's amplitude when cutting frequencies and thus can clip and crackle and pop, Bessel is much smoother in shape and in sound.