The foundation of the modern science is the level of accuracy and reproducibility of numbers that are often obtained on some fancy technological innovations. When fMRI and other brain imaging (non-invasive) techs came out, some people may consider them to reveal everything about the brain. Only later we discover that how to interpret the results seem to be a more important issue than the numbers themselves. This is true in linguistics too. We used to think praat can tell us many information accurately and we believe those results without doubting them. But when you've used them for a couple of years, you start to wonder: because something seems wrong.
This happened to me lately a lot. First is the discrepancies in numbers we observe from praat scripts that I wrote to get F0 values and those measured manually. There is always a difference. Then, when you do it by hand, when you set the ranges (say 75HZ to 500 HZ) differently (say 50-500), you get different F0 contours! And that affects some positions of the markings. The most ridiculous thing is that when I wrote another script to extract the F1 formant value out of hundreds and thousands of sound samples, the F1 came out (as verified by hand by our post-doc) different from the results obtained by hand! How bizarre! then we discovered two things led to this: one is the formant setting, the other, more importantly, is that when you measure F1 by hand, depend on how much you're zooming in in the viewing window, you get a different F1 every time! Sometimes the difference can be great as 200Hz. The moral of the story is of course that with any kind of machine, we can't simply take the numbers but we have to be more sophisticated about interpreting them, and the only thing you can do is to keep it consistent and be careful in your control, because there is no right or wrong in these differences (the different values are obtained because of the different computations going on in different methods, which really is not easy to say which one is more correct). In a word, you can take it as the truth just because a computer says so.
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