I work for Okika Technologies producing a programmable analog device called DynAMx. Its like an analog version of a digital FPGA.
One of the things DynAMx is good at is making a configurable audio device. One of the interesting features of the tools is a filter designer. You can see the tools at http://www.okikatechnologies.com/DynamxDesignLab.html. They are free to download at http://www.okikatechnologies.com/Downloads.html.
We are thinking of doing a Raspberry Pi addon that allows users to adjust the filter parameters and generate lots of audio effects. I wanted to ask for feedback from the forum first. Is this something that sounds interesting?