>> why 12 semitones? As you noted, other numbers like 19, 43, and obviously also 24, gives interesting ratios. My current understanding is that while human ea

>> why 12 semitones? As you noted, other numbers like 19, 43, and obviously also 24, gives interesting ratios. My current understanding is that while human ear is easily able to distinguish finer frequency ratios, singers aren't able to match vocals to much higher precisions. 19 may perhaps still work, but 43 I think would be out of question.