The Alembic Q filters and a wah are related but different.
The wah circuit is a tunable bandpass filter. It cuts everything above and below a particular frequency. When you rock the wah, it shifts the center frequency.
When you shift the center freq it sounds like a vocal sound because changing your mouth shape changes the volume of your mouth cavity, which similarly shifts the resonant frequency of your mouth.
The problem with a wah filter on your bass is that this kind of bandpass filter gives the best wah effect but it has the effect of wiping out the bass end of the sound spectrum (this is obvious if you run your bass through a Cry Baby).
The Alembic Q doesn't have this issue. The wah pedal makes it's center frequency by getting rid of everything above and below. The Q filter is a active semi-parametric filter. Part of it acts like a regular low-pass filter - it cuts frequencies past a certain frequency which is set by the value of the filter knob. When the knob is turned up the cutoff frequency is high; as you turn it down, the cutoff frequency shifts downward.
When the Q switch is in the low position (I'm talking about a 3 way Series circuit here, I'm not to sure on the other models), the filter has a shape like a regular passive tone control.
When you put the Q switch in the middle or high position, the circuit creates a medium or large resonant peak at the corner frequeny. So, the low end is still passed through normally and the high end is still cut off, but there's a big increase in the output level right around the center frequency. This gives that shifting frequency boost like a wah pedal that moves around as you turn the filter knob.
In a parametric eq circuit, there are many features of the filter design that you can adjust - center frequency, the width of the eq zone, the sharpness of the effect on the eq zone (this is the Q-factor) . There are even more factors like the symmetry of the filter slopes. So, the Q-filter is picking a musically useful set of characteristics to get a circuit that has a lot of effect without millions of knobs.
Incidentally, these characteristics are what all the trimpots on the BagEnd ELF Integrator (also designed by Ron Wickersham) are controlling. The Integrator can create the assymetrical sort of response that the Q-filter creates, with the intent of allowing the ELF system to be tweaked to optimize the characteristics of multiple speaker bass systems.
David Fung
