overtones

All instruments have an infinite number of overtones. The relationship of the overtones to the fundamental frequency is what makes your upright bass sound different from an oboe or a tuba or pipe organ or a human voice. It is also what makes your bass sound different from anybody else's.

Recording upright bass is basically a matter of using mic placement to select which of the overtones you want to keep and which you don't. An upright bass has a large "nearfield" space. Within this nearfield, which can exist up to maybe 6 feet around the instrument, moving the mic a few inches one way or the other can have a noticable and dramatic effect on the recorded sound, mostly because you are picking up some overtones more than others, since different parts of the instrument resonate with some overtones more strongly than others.

Outside the nearfield, the overtones blend and balance out and the sound becomes pretty consistent regardless of where the listener's head is, other than the fact that, further away, you will capture more reverberation and "room sound." This is presuming that you have an acoustically neutral room to record in (if you're not sure, you probably don't).

Where to put the mic is a matter entirely of personal preference, and is worth doing some experimenting. Because the upright bass has such a large nearfield, there are a lot of different sounds available, and some are likely to be much better than others.

But overtones are neither bad nor good, in and of themselves. they are simply the "tone" of the instrument.

Cheers.