PtFilter - Interactive Digital Filter Design Tool

PtFilter is an interactive animated digital filter design tool that can be used both in engineering design and education. PtFilter was created by Bicheng William Wu as possible replacement for X-pole.

PtFilter is no longer under development

The applet may or may not work.

  • Sample Screen shot
  • Applet version Currently, the applet only works for IIR filters with Butterworth approximation in Bilinear transform, but you can design highpass, lowpass, bandpass, bandstop filters.

The source code is not available for download as a jar file. A tar file of the .class files is available.

You could use a Java decompiler such as jode

tar -xf ptfilter.jar
cd ptfilter
jar -cf filter.jar `find . -name "*class"`
jode -d . filter.jar

The ptolemy java files could be recovered from the ptII svn repository, see

The ChangeLog at lists when changes were made.

PtFilter was implemented using classes from ptolemy/filter

ChangeLog says:

1999-11-24 00:47  cxh

* [r9573] /trunk/ptolemy/filter: removed filter, it is unused and

To check out the code, try:

svn co -r 9572 ptII

It is unlikely that the entire 1999 version of Ptolemy will compile under a recent version of Java, but it could be possible to grab just the files you need from the packages that are in the ptfilter.tar file.