Imagine you're working at your desk upstairs. You become distracted by a news programme from a downstairs radio: starting to pay attention you realise that you can clearly hear every single word.
Not surprising in some ways… but then again there's something rather fundamental to notice here. The sound starts from the radio's speaker downstairs and reaches you at the top of the house. The sound travels up the stairs, back along the landing and then up along another set of stairs to your lair. Not only could you hear the news up- and down-stairs, but you could probably hear it outside as well.
In day-to-day living we are surrounded by all kinds of different sounds. Just stop and listen. The lived-in world is awash with sounds: noise; music; speech; birdsong. Some of these, such as the noise from traffic or the sound of people talking or the radio playing are just there and we often don't even notice them. Of course, sounds don't just exist as a kind of backdrop to our lives. They also provide us with information. For example, you quickly learn to recognise, by the sounds, when bacon is cooking too quickly, when the kettle is coming to the boil or when the car is misfiring.