> In the case of the human voice, these overtones will all be harmonics, because they display relationships based on perfect integers. On non-biologic instruments (which display slight deviations from perfect numbers due to mechanical attributes like stiffness), the whole matrix will get stretched or compressed according to the deviation (or “inharmonicity”) factor

I'm not sure I understand an instrument made mostly of meat and cartilage and maybe a little phlegm can be more 'perfect' than a mechanical one.