wub filters

LOWPASS:
    cutoff = 2.1 + (4000.0 * wub * wub)
    resonance = 0.3 * wub

HIGHPASS:
    cutoff = 0.1 + 2000.0 - (1000.0 * wub)
    resonance = 0.5 * wub * wub

where wub is one of these:
    wub = fabs(cos(tick / (length / 8)))
    wub = (tick + (beat * (length / 4))) / length
    wub = 1.0 - (tick + (beat * (length / 4))) / length
    wub = fabs(sin(tick / (length/16)))
    wub = 1.0
(updated on every sample)