IS THIS CIRCUIT, AND DOES IT REALLY "BOOST" MIDS?
This kind of circuit is referred to as an LC Network
L stands for Inductance and C for capacitance. An LC Network does
not "boost" anything
but rather provides some interesting tonal filters, somewhat similar to
the old Gibson varitone. The cap and inductor are wired in series. As you
probably know, caps lets treble through easier than low frequencies. The
inductor does the opposite by allowing low frequencies to pass through easier
than treble. Lets say the cap allows frequencies over 1000 Hz to pass, and
the inductor allows frequencies under 200 Hz to pass. When the 2 are combined
in series they act as a kind of midrange filter. Here is a graph
obtained by running the circuit through a very expensive network analyzer.
As you can see the mid-cut is around 850 Hz, but this will vary somewhat depending upon other factors relating to your particular guitar circuit.