You are welcome! I enjoyed this topic and helping out. Keeps the brain active!
There is a Butterworth.class in both the jdsp and the iirj libraries.
You can look inside the JAR files with WinRAR.
The error “The type Butterworth is ambiguous” happens when two or more classes with the same name (Butterworth) are available and Java can’t tell which one to use.
Some of this is familiarity and experience in searching for answers and quickly iterating down to a solution.
Not a pro at this but can navigate my way through these challenges.
It is not always easy but gets easier and I enjoy the challenge.
All those imports may not be need for your example.
I like to experiment and commented these out and included the one that was needed.
Some of the gurus here may offer better insight.
:)