Thanks Moo. I had seen them before, but forgot about them. Reading through them now, it certainly describes a circuit similar the the generic Alembic SVF (state variable filter) based filter. The Wal "attack" control is functionally similar to the Alembic "Q" controls, except that it is set internally to a predetermined boost at the roll off, not adjustable by pot or switches on the front of the bass.
Comments based upon this description from the second link.
"The two tone knobs operate electronic low-pass filters whose roll-off frequencies vary with the position of the control. Fully clockwise at 10, the spectrum is full and flat. As the controls are backed off, the spectrums of the appropriate pick-ups are foreshortened (roll-off 12db/octave). Therefore, the dominant tone character varies throughout the entire range of the control. Pulling up the tone knobs produces a quasiparametric boost of about 10db to the harmonics which lie at or near the roll-off frequency set by the rotary position."
So it's likely a pickup - buffer - SVF - Vol/pan - active DI - Tx sort of signal path, needing at least 8 - 10 opamps. Not too hard to duplicate functionally, but whether the chosen parameters in someone else's design would mean it would sound the same is another story. And of course, you can't get the Wal pups....
