In fairness, the readme does state:

> A good microphone is needed, with a wide frequency range and preferably with a flat frequency response.

By 'preferably' I assume it's implied that it can curve-fit (whatever's needed, I know next to nothing about this) to a non-flat microphone response, as long as it's known, but if it's flat then no need.

If it's unknown (and non-flat or assumed non-flat because it's cheap and doesn't make any claims about it) then that's the real problem, no point trying to do anything because it's like trying to construct a level floor with a shoelace for a spirit level.