- All of the following classes are subclsses of FilterTemplate:
They are NOT subclasses of Filter, which exists only to return one of the FilterTemplate subclasses. I therfore use Filter.construct() rather than Filter()
Filter.construct figures out which filter subclass to create, creates it and returns it.
The different filter types can be created using Filter.construct(). I think I do this to that we get back an object of one of the Filter subclasses (PoleZeros, )