Low Pass  Treble Cut
 For DC and low frequencies, the capacitor has no effect.
 The DC and low frequency gain = Rf / R1.
 Well above the breakpoint frequency, the capacitor
reactance is very low.
 At high frequencies, the gain drops to zero due
to the negative feedback through the capacitor.
 The input resistance equals R1.

Treble Boost
 At low frequencies, the capacitor has no effect.
 At low frequencies, the gain = Rf / R1.
 At high frequencies the capacitor reduces R1.
 At high frequencies the gain increases.

High Pass  Bass Cut
 The capacitor blocks DC and low frequencies.
 The capacitor passes high frequencies easily.
 The amplifier provides gain.
 DC and low frequencies the gain = 0.
 Well above the breakpoint frequency, the gain = Rf / R1.

Bass Boost
 For DC and low frequencies, the capacitor has no effect.
 Rf must be large.
 At low frequencies the gain is large = Rf / R1.
 At high frequencies, Xc is low so the gain drops to zero.
 The input resistance equals R1
