Hi Hugo,
I just compared the frequency spectra of your recordings with the long-C-note audio recordings of Grec. The most prominent difference is right after the attack. In Grecs spectra I saw only the distortions caused by the metronome in the background. While your spectra contain clear visible distortions. Based on my own experience and experimenting: installing an audio spectrum analyzer on a smartphone is easy to do. The direct feedback of such an analyzer while playing makes it easier to find a way to reduce these distortions. The brass effect is stronger when playing louder according to the physics of a trumpet. It is fun to visualize this effect as an exercise with a spectrum analyzer. On my old beginners trumpet this effect is also much weaker when comparing with Grecs recording. I am not sure if this is due to my skills or a limitation of my trumpet.

René