If I keep the amplitude constant and up the frequency of the sound wave, what effect does just the frequency have on the quality of the sound with regard to human hearing?
Does the sound become shriller in tone?
The sound becomes higher in pitch. Pitch is, basically, just frequency.
"Shriller" is one way to describe this, although it carries a somewhat negative connotation.
I think decreasing sound frequency will spread the sound over longer duration and vice-versa. So if you increase the frequency, on time axis, the sound wave should compress and you can hear the sound at faster speed or at rate of more than 1 (it’s just like what we often do in diff media players... we increase the speed at 1.2 / 1.5 etc. and conversation becomes faster. This is actually done by increasing sound frequency).