The Phonics library has been made public on GitHub. The library is the code used to procedurally generate the audio data in the WebKeys app.
While it was designed to be used for Unity to calculate streaming AudioClip PCM sample data, in theory it should be usable outside of Unity. Although because it’s made for Unity, note that it only supports generating single precision floating point PCM (aka floats).
It also contains the utility functions for calculating the audio frequencies of (western) 12-tone equal temperament notes.
It’s not a mature library, so if anyone uses it expect some volatility in its interface. Documentation and code comments to come soon.
Edit 4/02/2022: The whole ‘to come soon’ thing may have been an accidental lie…