Thank you for a (really) quick answer.
Well, actually it does not help.
1. Although the BWs of filters are limited but they cover the whole spectrum (at least they should)
2. It seems you make some kind of (light) averaging in each filter - the noise is cancelled pulling out stable signals (if there are any)
Have a look at the picture. I suppose it's self-explanatory, but for clarity it is the amplitude exponential rise of pink noise followed by 1 kHz sine wave step-down in 10 dB steps.
Again, these are my laic reverse engineering thoughts, but ...