Shouting out to some classic software I have used for the Elektron Machinedrum UW. First up is a sample editor called UWEdit. UWEdit allows you to do some advanced prepping for your samples on your computer.
In the software you load an audio WAV file and convert it to a SYX sysex file. The SYX file can then be transferred to and played by the the MachineDrum UW. You can also precisely set loop points. With the limited memory of the MD UW, loop points can really help you incorporate some nice “long” samples in the MD. You can also provide a four character name for the sample. Even 4 characters for naming is a big step up from the very old days where no naming was possible in the MD UW. You can also set the Slot number where you want the sample to be located. This is nice because it is easier to do here than menu surfing in the MD.
The latest version is 0.9a released in 2011 by E. Heidt. There are Windows and Mac versions available. Head on over to https://code.google.com/archive/p/uwedit/ for more information and downloads.