I just tried to make a monotonous sound with my vocal chords while changing my mouth cavity to a melody, like in the "chhh" experiment, or as if I were whistlin

I just tried to make a monotonous sound with my vocal chords while changing my mouth cavity to a melody, like in the "chhh" experiment, or as if I were whistling, and for me it's kind of impossible. If my vocal chords are vibrating, then the pitch they make follows my mouth shape. I'm wondering did you need to practice that?