-The efficiency of an audio amplifier is expressed
as power out divided by power in, but it can be expressed as a percent
by multiplying power out by 100.

--the cutoff frequency of a lpf or hpf, but I refer
here to an lpf. They are esentially the same in resistance capacitance
constants.

Fo = 1 / (2 pi R C) where Fo = cutoff frequency in HZ pi = you know, the number that makes a more accurate equation the
more digits it uses. r is the ohms of resistance prior to the capacitor c is the farads of capacitance connected to ground

for example if you have a 100k resistor and a 10nf
capacitor (same as .01 microfarad) connected to a buffer the cutoff
will be approximately 159hz 2 X 3.14 X 100,000 X .00000001 = .00628 1/.00628 is close to 159

--To make a linear volume control exponential place
a resistor to ground on it's output path, the middle terminal.
This works if there is no resistance prior to the potentiometer. The
resistor must maintain a ratio of 100 to 15, if the full value of the
control is 100k ohms the resistor must be 15k. This can actually be
more accurate than a cheap audio taper but can also cause problems if
done in a complex circuit.