One definition we could give is that what we perceive as being sound is a variation in relation to a constant value, of air pressure.

In the previous paragraph we saw how the flow of atmospheric pressure in relation to the active loudspeaker can be visualized as a waveform. Waveforms can actually be very complicated, but fortunately every single one of them, and I mean every single one, can be considered as an extension of a very simple wave form: the sinusoid