Logbook - Houston, we have a solution (maybe this thing was already known but if in doubt I'll write this mini guide).
For all those who would like to create sounds from scratch but have difficulty finding suitable samples and you don't have Adobe Audition, there is a solution: Reaper.
This DAW (Digital Audio Workstation) has a feature called pitch envelope which works similarly to Audition's pitch bend. Simply load the sample you recorded into the software and follow the following steps:
1) double click on the track and untick the item circled in the picture 1;
2) right click on the track > take > take pitch envelope;
3) right click on the pitch line and add the necessary points according to the track;
4) manage the line in order to obtain a uniform pitch;
Remember to set the envelope range to 10 or 12 semitones (options > preferences, picture 2). In my case the range is 16 but 10/12 is enough. Reaper is offered with an initial trial period of 60 days, but re-downloading the software resets the counter (at least as far as I tried it worked).
Obviously the sample must be adapted so that it can be played in a loop, so the good audacity must still be used before bringing everything into Fmod.