[PD] gain normalization help?

[David Merrill]

Hi there -
I'm buildng a patch that features a chain of DSP operators being applied 
to a signal (volume, sweeping bandpass filter, tremolo, delay, etc..) 
and something that I've realized about the bandpass filter is that it 
affects the overall volume of the sound (even when the signal coming 
through has most - but not all - of its spectal energy at the center 
frequency) - which makes sense. I want to be able to switch the bandpass 
on and off, but keep the overall gain of the mix constant. Is there a 
preferred, canonical way to normalize gain and keep it relatively 
constant? (maybe something involving an env~ object..)
thanks,
David M.