You could also try using the more CPU friendly version of the ladder filter as Richard van Hoesel outlined here. I recently used it on a Adafruit ItsyBitsy M4 Express board and it worked well. I applied his changes and stuck the files on my...
Seems like you're making good headway with Pio in the other thread. I was going to mention before I saw Pio's progress - if you’re wanting to change the delay time on the fly, it might be better to start with houtson's delay10tap object or...