I tried to make a custom unit that features two filters (LP & HP) yesterday evening, with a separate input to both filters. So you could do a kind of filter controlled crossfade.
So custom unit with 4 linear control:
External Square wave to linear in 1
External Saw wave to linear in 2
Linear in 3 mapped to control cutoff of both HP and LP
Linear in 4 mapped to control res of both HP and LP
Linear 1 as input to the LP (which is actually within a mixer chain)
Linear 2 as input to the HP (which is also within a mixer chain)
All good so far.
The first problem I had was the sweep of the value on linear 3 was too violent and extreme. My guess is this because I have linear control of frequency, when maybe exponential would be better, what would be the best way to achieve this? swap linear 3 for custom control of the pitch type? The second issue is that the high pass filter still allowed quite a lot of signal from the saw through even when set to its maximum value of 13Khz.