I have a preference for blowing a shofar that produces a clear low pitched sound. (Of course, when I choose a shofar, my higher priority is that it's lightweight and is easy for me to blow.)
O.C. 586:6 (Thanks DoubleAA for providing ref) says that "all types of voices" are considered kosher, meaning that if the sounds is dull or "heavy", they are valid.
I'm curious if outside of halacha, are there any other sources stating any recommendations regarding the preferred or "ideal" sound quality of the shofar, and what the reasons would be.