Hi,
it falls 6db/octave means:
* falls = minus
* minus 6db = -6dB = 10 ^(-6/20) = 0.5 (as factor) = 50%
* one octave (like in music) is doube (or half) the frequency.
Now the formula 6db/octave means: with double the frequency you get half of the amplitude.
This is the behaviour of an integrator, or the behaviour of a first order low_pass_filter in stop band.
Example:
let´s say the amplitude at 440Hz is 1V (music: standard "A")
Then at double the frequency it is half the amplitude: 880Hz --> half of 1V = 0.5V (the next higher "A")
and further 1760Hz --> half of 0.5V = 0.25V (again the next higher "A")
and so on.
In general: multiply the frequency with x, then you get 1/x of the amplitude. (= you have to divide the amplitude by x)
Added: indeed 6dB is not exact: it should be -6.0206... but to ease this we simply say 6dB.
Klaus