There are good reasons for saying hello.
I fully support being polite, but there's a lot more to vowels than relative pitch.  When speaking a vowel, the geometry of your mouth creates multiple resonant frequencies.  The ratio among those frequencies is far more important than the ratio of the dominant frequency of one vowel to the dominant frequency of the next.Consider a couple of examples:1. A trombone can't say "I Owe You", despite the fact that it can produce any dominant frequency, and that phrase contains only vowels.2. Voice "Ahhhhhhhhhhhh", going from a high to a low pitch (I imagine the doppler effect of a cartoon screaming as he rides by on a cart), and then voice "Ohhhhhhhhhhhhhh" in the same fashion.  At every point, they sound different.  You can't take a clip from an arbitrary pitch range of an Ah and convince someone its an Oh.3. Shape your lips like you would for oo as in Moon, Noon, or Spoon, and try make the ea vowel as in Squeak just by changing your pitch.  It won't happen.  You'll get the German ö, but not the English ea.