If a robotic vacuum cleaner works while no one is home, does it still make a sound? That new spin on the tree falling in the forest may not inspire you to a night course in philosophy, but it does underscore an important point in the realm of sound quality: there is a distinction between the objective reality and the subjective experience. The former relates to the physical phenomenon of generating sound pressure waves that can be quantified and characterized by a variety of standard metrics such as intensity level, frequency, harmonics, and so on. This objective aspect is often referred to as noise.