Poles & Zeros is a freeform digital filter designer utility that lets you directly interact with z-plane poles and zeros, instead of utilizing a parametric approach. While providing instant feedback about the frequency response, the application also supports realtime audio previewing (using built-in waveforms). The high-precision audio engine enables the interactive exploration of systems containing relatively high numbers of poles and zeros - and comes with adjustable accuracy so the right priorities can be set when working with computationally intensive high-order digital filters.
Visualization options include impulse & step responses, plus the 3-dimensional transfer function graph. Other features include direct / cascade realizations with C code generation, and save / recall functionality with on-the-fly loading (when the audio preview mode is active, you can instantly listen to any saved filter as you browse through the list).
Please note that only even-order filters are supported.