This ability is called “selective hearing” and is a computational function in your brain that enables you to focus in on your companion’s voice in the midst of the endless sound waves coming from ceiling fans, ambient music, and other people’s voices bouncing off the walls. Your ability to focus in on that single selected voice is impressive.
Although most modern humans are no longer engaged in hunting and gathering activities, our world would look very different were it not for selective hearing. Imagine living in a city – or even a moderately sized suburban town, for that matter – with its ambient atmosphere combining traffic, voices, weather sounds such as wind or rain, and the rest of the cacophony of daily life that we simply don’t think about from moment to moment. Were it not for selective hearing, we would drown in an overwhelming sea of noise, unable to focus on any one sound well enough to effectively evaluate its importance. Considered in that context, the neurological capability that we call selective hearing has played a significant role in defining how we function as a species.