X4 sType filters may cause step in output when turning off.
The source code for handling filter switching on/off is in src/include/drv/fm10gen.c around line 1080.
When requested to turn on or off, filters where sType has '4' in the second digit wait to turn on until the input is near zero, and wait to turn off until the output is near zero.
Every filter acts as a bypass when it is turned off, however, sending its input along to the next filter. This input may not be near zero when the output is near zero, which would lead to a step in the output.
Suggestions: Have sType '4' filters act as sType '3' filters when turning off: wait until output and input coincide.
Switch all filters to sType '3', since '3' already nicely handles the case when turning on where the output is a steady zero.
On a related issue, both '3' and '4' have a timeout. When the timeout expires, the filter is switched on immediately, causing a step. It might be a good idea to fallback to a ramp.