I use Captura. The UI is not very accessible but I set everything up in the JSON config file manually so that when I press Alt+F9 globally, it starts and stops recording of screen, microphone, system audio, and a log of timestamped keystrokes.

Let me know if a sample config file would be helpful.

Filling out the frequency spectrum is not quite useful, white, pink and brown noise do that already with some changes to the lower frequencies for the two latter ones.

What you are looking for is an even distribution of the existing frequencies (Teote, Ozone, Hornet Thirty-one, WavesFactory Equalizer, Grand Finale, DSEQ3, Gullfoss, etc) do this, exciters and saturation to add new harmonic content, just to mention a few things. Ultimately, these tools, despite the aggressive marketing some of them have, can't replace your ears but they provide fast results if you don't want to focus on mixing and mastering. You still need to tweak things and it's very easy to overprocess your sound of course.

Several books could be written about how many things could influence your sound, both while mixing and mastering (from the headphones or monitors you use through the room you are in, to what your genre needs), not to mention when your final master reaches your listeners. Their hardware, environment, ears, etc, will color the sound as well. You could have a perfectly neutral master and someone could quite easily make it heavy on bass just by listening to it on gaming headphones, or better yet, listen to it in a car.

This is a very complex and overwhelming topic, but if you need advice and you really want to make your sound better, listen to the same genre as much as you can. That's how you train your ears to get accustomed to things that stick out (resonate) and over time you will learn what instrument is problematic in what specific frequency areas. Most importantly, less is more.