To... um... amplify on that a bit:

Assume a circuit where there is a voltage amplifier of gain Vg, with input resistance Rin and some capacitance Cin from the input to ground. The signal source impedance Rs (presumed resistive to a first order for audio) reacts with that input capacitance to form a low pass filter. The input resistance of the amplifier is in parallel with the capacitance to ground.

At frequencies where the capacitor doesn't shunt the signal to ground, the amplifier gain is unaffected by the capacitor. At very high frequencies, the cap to ground acts like a more-or-less dead short, shunting all of the input signal current to ground. The frequency at which this starts to happen can be computed, and for amplifiers which have Rin much larger than Rs is F = 1/(2*pi*Rs*Cin), just the rolloff frequency of the Rs and Cin. If Rin is not much greater than Rs, it can still be computed easily, but you can't ignore Rin.

Cin "eats" some of the signal current by shunting it to ground away from the input terminal. We'll come back to this concept in a minute.

Let's further assume that the amplifier is inverting, and has some feedback capacitance Cf.

The feedback capacitor has a voltage on the output side of -Vg*Vin (the amplifier is inverting) and on its input side of Vin. So the total voltage across it is Vin - (-Vg*Vin) or Vin * (1+Vg).

For AC signals, a current must flow through the feedback cap. That current is the voltage acrosss the cap divided by the cap's impedance, or Icf = Vin * (1+Vg) . This currrent must come out of the input node - the output of the amplifier is sucking current away from its input.

Remember Cin? It too is sucking current away from the input. The current it sucks is Vin/Xcin. The feedback cap sucks (Vin/Xcf)*(1+Vg).

So a feedback cap sucks current away from the input of the same amount as an input capacitor to ground that is the voltage gain plus one times larger. That is,

*A feedback cap looks to the circuit like an input capacitor that is the voltage gain times larger.* The capacitor has been "multiplied" by the voltage gain of the circuit. It is common to ignore the "1+" because for gains over ten, it makes no significant contribution.

There are other places where voltage gain multiplication of capacitance happens, notably in the Vox Wah circuit - see "The Technology of Wah Pedals" at GEO.