Q actually does stand for Quality when discussing filters. It doesn't seem to be really accurately applied here, though. The Q of a filter increases as the width of frequencies it applies to decreases.
In a parametric EQ, you would have three controls. One that controls the target frequency of the filter, one that controls the amount of cut/gain to be applied, and one that controls the Q, or width of the frequency range that is impacted.
Here's where it starts not to make too much sense for me. Consider the rest of this post to be speculation rather than fact.
As I understand it, the frequency response through an Alembic filter should look like a flat line that ends at the top of a slide. The point where the flat line and the slide meet is adjustable by turning the filter control to any frequency between 350 Hz and 6000 Hz, as per Val's earlier post. When you turn the Q switch on, you get about a relatively narrow 8 db bump centered on the frequency where the slide begins.
There is also a three-way Q switch on some instruments that gives you a choice between two bump sizes when it is on, and the CVQ (Continuously Variable Q) found on the Series II that lets you adjust your bump size anywhere from 0 to 15 db.
All this makes the Alembic filter seem to be a strange beast, like two filters in one. It seems that there is a low-pass filter that reduces gain above the selected frequency. It also seems that there is a narrow band-pass filter that is activated with a boost when the Q switch is enabled. With the Q switch off, the band-pass filter is effectively off as well. Both filters share the same control for selecting their frequency.
I have no idea how it is implemented electronically, but this seems the best way to describe it based upon my understanding of what it does. Does this make any sense?
