Pick-Direction Lowpass Filter

The EKS pick-direction lowpass filter is simply a unity-dc-gain one-pole filter with a different coefficient for an ``up-pick'' than for a ``down-pick''. Thus, the filter transfer function is

$$H_p(z) \;=\;\frac{1-p}{1 - p\,z^{-1}}$$

where $p$ takes on two different (real) values (such as 0 and 0.9), depending on the picking direction. The idea is that real up-picks may be at different angles than down-picks, thus resulting in different plucking stiffness, among other possible effects.

In Faust, a unity-dc-gain one-pole filter can be defined by

    pickdir =  *(1.0-(p)) : + ~ *(p);

where p is the pole location. This pole position can be modulated by a pick-direction ``toggle'' signal as follows:

    p = 0.9 * checkbox("pick_direction"); // [0 or 0.9]