Bass Whistle iPlug 2 Plugin
Fork of iPlug2 which adds Bass Whistle
To use this, follow an iPlug2 tutorial. To build a VST3 for Reaper you'll need to download the VST3 SDK and manually copy it into the dependencies directory.
The main code for BassWhistle is in https://github.com/jeffkaufman/pitch-detect/blob/master/zeros.c This is a fork of both that and of iPlug2 which allows it to be used as a VST3 in Reaper.
I should probably make zeros.c more of a library and allow this to include it as a submodule, but for now the code is copied and tweaked to work in the new environment.