[LAU] DSP filter design tools?

[Mark Knecht]

Hi all,
   I wonder if there are any Open Source tools for learning
software-oriented DSP, most specifically designing filters?

   I'm an EE but haven't done any real math in years. I just want to
fool around, write some equations, see the results in some sort of
frequency (filter characteristics) or time (impulse response) plots.

   Does anything like that exist?

   I started looking at Octave but it's clearly over-kill so I figured
I'd ask if there was a better platform?

Thanks,
Mark