We hear mainly through our ears which respond over a frequency range of around 20Khz. Stereo is important to many human actions and even the phase difference between signals arriving from the same source at each ear (as well as simple timing, since sound moves so slow compared with light) gives us good directional hearing, although mainly at high frequencies. As people et older, their high frequency accuracy decreases quite markedly, although this doesn't usually affect speech recognition until old age.