In nearly every digital recording I make, the background noise is loudest
at the very bottom of the spectrum. 0-40 Hz can contain more signal than
40-20K Hz.

Playing with the rolloff filtering today, I found that starting the rolloff
much higher and using a low filter value yielded a smoother bass.

Whereas I often rolloff below 30 Hz using an 18th order Butterworth filter,
this time I tried from 80 Hz using a 4th order filter. I lost just a touch
of the bass drum, but the remaining sound is more pleasing.