LP4 filter roll off of Ripples

Spent the afternoon with my modular and the awesome SubPac http://thesubpac.com/what-is-the-subpac/ frequency response range from 5hz-130hz

Something I’m wondering is with Ripples LP4 (Cutoff frequency, 18Hz to 18kHz) completely cutoff there is still quite a bit of bass creeping through to the subpac - effectively this means information is still being recorded and added and multiplied in mixes where I use these recordings.

However, the same audio through my 5U Dotcom Ladder Filter (Frequency Range: 20hz to 20khz) completely cut results in no audio making it to the subpac, no feeling or bass vibrations.

Why does the Ladder Filter cut complete and not Ripples?

Um, a low-pass filter, as the name suggests, allows frequencies below the cut-off point to pass, thus surely you would expect to hear or feel very low frequencies passed through it. Also, filters have roll-off slopes, so they still pass frequencies above the cut-off point, but just with increasingly lower amplitudes. Thus, with a 24dB/octave filter, and the filter cut-off set to 18Hz, you will still hear signals at 36Hz, but just 24dB quieter than otherwise.

> Why does the Ladder Filter cut complete and not Ripples?

Probably because the 20 Hz to 20kHz is a nominal figure and it’s actually going lower than that - the minimum cutoff might be much lower (maybe 5 Hz) so that the lowest audio frequencies are actually attenuated enough to disappear.

Thanks guys, very informative answers.