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

where 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]

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written by Julius Orion Smith III
Julius Smith's background is in electrical engineering (BS Rice 1975, PhD Stanford 1983). He is presently Professor of Music and Associate Professor (by courtesy) of Electrical Engineering at Stanford's Center for Computer Research in Music and Acoustics (CCRMA), teaching courses and pursuing research related to signal processing applied to music and audio systems. See http://ccrma.stanford.edu/~jos/ for details.