Mira el crossover de RS-Met, es gratis y hace lo que quieres:

CrossOver is a plugin to split an incoming signal into several (at most 4) frequency ranges. It can be used to build your own multiband effects within a modular (sub)host environment. By using only 2 bands, you can also create bass-effects. These are effects which keep the low frequency range dry and affect only the high frequency range. The band-splitting is done by complementary pairs of Linkwitz-Riley lowpass/highpass filters, the slope of which is adjustable between 12 and 96 dB/oct. For configurations with more than 2 output bands, the signal is first split into 2 bands (low and high) and then the low or high or both bands is/are split further, thus the splitting is done in a hierarchical manner.
RS-MET