Linear Prediction Coder
an open source au- & vst-plugin that does linear prediction coding and pitch shifting. sounds crazy on voice.
now for mac only but should be easy to compile from source for Windows as well.
for macOS 10.11. move the file to ~/Library/Audio/Plug-Ins/Components to install.
for macOS 10.11. move the file to ~/Library/Audio/Plug-Ins/VST3 to install.
source is on github