Addressing "How does a phaser change from Stun to Kill?"
The Star Trek the Next Generation Technical (isbn 0-671-70427-3) Manual covers the power settings.
The differences in the settings are based on power output and duration, as well as SEM (Simple Electro-Magnetic) and NDF Nuclear Disruption Force ratios.
I don't want to quote the whole article (plagiarism/copyright) but here are some settings listed:
For personal phasers:
- Setting 1: Light Stun - discharge energy index 15.75 for .025 seconds. SEM:NDF ratio N/A (Calibrated for base humanoid physiology)
- Setting 2: Medium Stun: Discharge energy 45.30 for .075 seconds SEM:NDF ratio N/A
- Setting 3 (Heavy Stun) Discharge energy 160.65 for 1.025 seconds SEM:NDF ratio N/A
- Setting 4 (Thermal Effects) Discharge energy 515.75 for 1.5 seconds SEM:NDF ratio N/A
...
At setting 6, disruption effects kick in, introducing the SEM:NDF ratios on up through
- Setting 10: Disruption Effect, Discharge energy 125,000 for 1.3 seconds SEM:NDF ratio 1:9
Addressing the audible effects issue, itAddressing the audible effects issue
It seems to me that since these give different energy outputs, the sound would be different. A blender on setting 4 makes a different sound than one at setting 5, etc.
I can usually tell the difference between the sound of a .22 rifle, a 9mm, and a .45 caliber (although that's only because they get drastically louder as you go).
I can definitely tell the difference between different fans that we have in our house.
Someone trained in the use of these weapons should be able to tell the difference between the settings by sound as well.