ok.
This is the official address of the JDSP library, JDSP - Digital Signal Processing in Java
a Java library for digital signal processing.
Just a plain java library, not specifically designed for processing.
This is explained in the old version of the official GitHub repository
How to Install a Contributed Library · processing/processing Wiki
Non-Processing Libraries
Another example: you want to use the Apache Common Collections library, which is a plain Java library (ie. not designed for use with Processing). The zip file contains a folder named commons-collections-3.2.1 with various files in it, including one: commons-collections-3.2.1.jar
You have to create the libraries/ApacheCommonCollections/library folder (the middle name can vary, but must have only letters and numbers) where you put the jar file renamed along the folder name (here, ApacheCommonCollections.jar, then).
Alternatively, if you need this library for only one sketch, you can just drag’n’drop the jar file on the PDE, it will put it in a folder named
codein the sketch folder (you can also create the folder manually and put the jar file there yourself). This also works, of course, for regular Processing libraries. This solution isn’t optimal if you plan to use the library in several sketches, as it will duplicate the library, taking up space and making difficult a possible upgrade.