There is one setting in the S5 which can make a small different in the way your voice will be heard to the person on the receiving end. This setting was never created to adjust your voice sound in any way (that is all handle in the carrier’s own network) but does offer some control effect.
1. Go to settings
2. Then tap Sound
3. Scroll down to Call and tap.
4. Locate Noise reduction and if you check this box it will suppress some breath sounds and background noise in your talking area.
When this box is unchecked however it also will allow a slight increase in your voice input but at the possible cost of more noise pickup. Your base audio is controlled by your phone and the network and can't be changed as posted. When using my own S5 with this setting on, I have been told by callers that my voice was clear while on the Verizon Network. In the off position they reported and I have recorded a somewhat stronger voice but with a very small hiss sound in the background.