Some time ago, I discovered what I think is a bug with Spire's filter when using filter keytracking. It's really easy to reproduce: Press the init button to initialize a patch, choose a lowpass filter (Infecto or Perfecto), set the keytracking to 1.000 (100%), dial in about 60 or 70 % filter envelope decay, sustain to zero or a low value, release to full amount, add a lot of resonance to make the issue more apparent, play a note C-1 or lower, and then play with the filter cutoff, and notice how the filter won't close anymore when you reach a value of about 200 or lower. When you play lower notes, there's a even bigger parameter area where nothing happens. Also, the keytracking stops working at that point.
See this video as demonstration: https://1drv.ms/v/s!Asq_J3FOGuuFnGxgcr8 ... y?e=xL0oM0
Also try to play lower notes, first C-1, then C-0, and notice how the parameter area of the filter cutoff in which nothing happens gets bigger. For me, this is clearly a bug, as none of my other synths does this.
