As far as architecture and acoustics go, the venues of Indianapolis concerts don’t have a lot in common. There are giant arenas, nationally renowned blues clubs, and intimate lounges. But whether you’re listening to Keith Richards wail an anthemic riff at Bankers Life Fieldhouse or an up-and-coming artist strum an intimate ballad at Hi-Fi, the sound reaches your ears in the exact same way: in waves.

When a guitarist plucks a note, the string causes the air molecules around it to vibrate, which in turn causes more molecules to vibrate, and on and on until the wave reaches your ears. The differences in the way we perceive these waves—that is, the variations of sound—are largely because of a few key characteristics:

Amplitude

How loud or intense a given sound is entirely depends on its amplitude, which is easily visualized as the height of the wave from crest to valley.

Frequency

Defined as the speed at which each crest of the wave passes any given point, the frequency determines a sound's pitch. Lower pitches have lower frequencies and spaced-out crests, whereas high frequencies appear as tight zigzags.

Uniformity

For the most part, the distinction between our perception of a noise and a musical tone is based on how consistent the wave is: noise is unpredictable and jagged, like a choppy sea, while a tone flows steadily, like a tide lapping on the sand.

Medium

As a pressure wave, sound can travel through almost any medium, from water to solid rock, though each medium affects the speed (and distance) at which the wave can travel. A major exception is in a vacuum, where no air means no molecules to vibrate and propagate the wave.

OK, so that’s how sound works. Then how do ears work?

Aside from their ability to make the wearing of shutter shades possible, ears are delicately, exquisitely attuned to receive and translate sound waves. Their dish-like shape conducts sound into the ear canal, where it encounters the eardrum—a tiny, thin membrane that vibrates at the same amplitude and frequency as the waves themselves. Then, in the middle ear, the three smallest bones in the entire human body take on the very large job of converting that vibration into mechanical energy.

From there, the wave flows through the fluid contained in a coiled tube called the cochlea. It’s lined with tiny hairs, each tuned to a specific frequency. Once a wave finds a hair with a matching frequency, a nerve impulse alerts the brain to recognize the sound, and the process is complete.