From Mr Q himself, page 27: "The two Bass Block EQ knobs are:
DEPTH: an active cut-boost bass control, with 12 dB of range and an unusually low hinge frequency of 100Hz, and a very high slope (24dB/octave) to provide pinpoint control of the relative loudness of the lowest strings and overall roundness of tone. This is coupled with a unique 2-stage limiter that prevents obtrusive “bottoming out”, even with heavy bass boost, without the lag or “gagging” effect of conventional limiters. High amounts of GAIN will produce a musically interesting “thrumming” or growling effect without actual hard clipping.
CONTOUR: the left side provides a 12dB mid cut at 300Hz, which tames the “bark” frequencies and leaves a nice “plicky” sound for a refined “studio” tone. The control is flat in the middle, and the right side engages a deep treble cut at 200Hz for a fully rounded old-school tone."
So, 100Hz.