Headsets fitted with 2 wires use your computer’s sound card. If your sound card is of lesser quality, the sound of your voice will also be of lesser quality regardless of the quality of your headset. There may also be a lot of static accumulated on your card, which gives you a “robotic” voice. For optimal sound, we strongly suggest buying a USB headset to avoid any problems related to the sound card.
If you are already using a USB headset, but it produces a constant low-pitched sound, try a different USB port. You may also want to test the same USB headset on another computer. If the problem persists, it is probably caused by a material problem. Contact your USB headset manufacturer in this last case.