Originally Posted by jehymel
The problem with gain is that it boosts the entire frequency spectrum, not just your voice. This results in the road/exhaust noise being amplified at the same level as your voice, so it is in effect just turning the volume "up" for the person on the other end of the line.
This gives me an idea: would it possible to put in a high / low pass filter to allow only human voice to pass through? I'm not a DSP guy, but maybe I can talk to some of the electrical engineers I work with and see if this is possible.
Edit: Oh, I tried adjusting the gain on the way home from work and my sister claims it didn't make any change.